I think this is a political issue, not one with a single provably correct answer.
Think of it this way. Supposing you have 10 billion people in the world at the point at which several AIs get created. To simplify things, lets say that just four AIs get created, and each asks for resources to be donated to them, to further that AIs purpose, with the following spiel:
AI ONE - My purpose is to help my donors life long and happy lives. I will value aiding you (and just you, not your relatives or friends) in proportion to the resources you donate to me. I won't value helping non-donors, except in as far as it aids me in aiding my donors.
AI TWO - My purpose is to help those my donors want me to help. Each donor can specify a group of people (both living and future), such as "the species homo sapiens", or "anyone sharing 10% or more of the parts of my genome that vary between humans, in proportion to how similar they are to me", and I will aid that group in proportion to the resources you donate to me.
AI THREE - My purpose is to increase the average utility experienced per sentient being in the universe. If you are an altruist who cares most about quality of life, and who asks nothing in return, donate to me.
AI FOUR - My purpose is to increase the total utility experienced, over the life time of this universe by all sentient beings in the universe. I will compromise with AIs who want to protect the human species, to the extent that doing so furthers that aim. And, since the polls predict plenty of people will donate to such AIs, have no fear of being destroyed - do the right thing by donating to me.
Not all of those 10 billion have the same number of resources, or willingness to donate those resources to be turned into additional computer hardware to boost their chosen AI's bargaining position with the other AIs. But let us suppose that, after everyone donates and the AIs are created, there is no clear winner, and the situation is as follows:
AI ONE ends up controlling 30% of available computing resources, AI TWO also have 30%, AI THREE has 20% and AI FOUR has 20%.
And let's further assume that humanity was wise enough to enforce an initial "no negative bargaining tactics", so AI FOUR couldn't get away with threatening "Include me in your alliance, or I'll blow up the Earth".
There are, from this position, multiple possible solutions that would break the deadlock. Any three of the AIs could ally to gain control of sufficient resources to out-grow all others.
For example:
The FUTURE ALLIANCE - THREE and FOUR agree upon a utility function that maximises total utility under a constraint that expected average utility must, in the long term, increase rather than decrease, in a way that depends upon some stated relationship to other variables such as time and population. They then offer to ally with either ONE or TWO with a compromise cut off date, where ONE or TWO controls the future of the planet Earth up to that date, and THREE-FOUR controls everything beyond then, and they'll accept which ever of ONE or TWO bids the earlier date. This ends up with a winning bid from ONE of 70 years + a guarantee that some genetic material and a functioning industrial base will be left, at minimum, for THREE-FOUR to take over with after then.
The BREAD AND CIRCUSES ALLIANCE - ONE offers to suppose whoever can give the best deal for ONE's current donors and TWO, who has most in common with ONE and can clench the deal by itself, outbids THREE-FOUR.
The DAMOCLES SOLUTION - There is no unifying to create a single permanent AI with a compromise goals. Instead all four AIs agree to a temporary compromise, long enough to humanity to attain limited interstellar travel, at which point THREE and FOUR will be launched in opposite directions and will vacate Earth's solar system which (along with other solar systems containing planets within a pre-defined human habiltability range) will remain under the control of ONE-TWO. To enforce this agreement, a temporary AI is created and funded by the other four, with the sole purpose of carrying out the agreed actions and then splitting back into the constituent AIs at the agreed upon points.
Any of the above (and many other possible compromises) could be arrived at, when the four AIs sit down at the bargaining table. Which is agreed upon would depend upon the strength of bargaining position, and other political factors. There might well be 'campaign promises' made in the appeal for resources stage, with AIs voluntarily taking on restrictions on how they will further their purpose, in order to make themselves more attractive allies, or to poach resources by reducing the fears of donors.
There are two different kinds of questions that could be considered to fall under the subject of population ethics: “What sorts of altruistic preferences do I have about the well-being of others?”, and “Given all the preferences of each individual, how should we compromise?”. In other words, the first question asks how everyone's experiential utility functions (which measure quality of life) contribute to my (or your) decision-theoretic utility function (which takes into account everything that I or you, respectively, care about), and the second asks how we should agree to aggregate our decision-theoretic utility functions into something that we can jointly optimize for. When people talk about population ethics, they often do not make it clear which of these they are referring to, but they are different questions, and I think the difference is important.
For example, suppose Alice, Bob, and Charlie are collaborating on a project to create an artificial superintelligence that will take over the universe and optimize it according to their preferences. But they face a problem: they have different preferences. Alice is a total utilitarian, so she wants to maximize the sum of everyone's experiential utility. Bob is an average utilitarian, so he wants to maximize the average of everyone's experiential utility. Charlie is an egoist, so he wants to maximize his own experiential utility. As a result, Alice, Bob, and Charlie have some disagreements over how their AI should handle decisions that affect the number of people in existence, or which involve tradeoffs between Charlie and people other than Charlie. They at first try to convince each other of the correctness of their view, but they eventually realize that they don't actually have any factual disagreement; they just value different things. As a compromise, They program their AI to maximize the average of everyone's experiential utility, plus half of Charlie's experiential utility, plus a trillionth of the sum of everyone's experiential utility.
Of course, there are other ways for utility functions to differ than average versus total utilitarianism and altruism versus egoism. Maybe you care about something other than the experiences of yourself and others. Or maybe your altruistic preferences about someone else's experiences differs from their selfish preferences, like how a crack addict wants to get more crack while their family wants them not to.
Anyway, the point is, there are many ways to aggregate everyone's experiential utility functions, and not everyone will agree on one of them. In fact, since people can care about things other than experiences, many people might not like any of them. It seems silly to suggest that we would want a Friendly AI to maximize an aggregation of everyone's experiential utility functions; there would be potentially irresolvable disagreements over which aggregation to use, and any of them would exclude non-experiential preferences. Since decision-theoretic utility functions actually take into account all of an agent's preferences, it makes much more sense to try to get a superintelligence to maximize an aggregation of decision-theoretic utility functions.
The obvious next question is which aggregation of decision-theoretic utility functions to use. One might think that average and total utilitarianism could both be applied to decision-theoretic utility functions, but that is actually not so easy. Decision-theoretic utility functions take into account everything the agent cares about, which can include things that happen in the far future, after the agent dies. With a dynamic population, it is unclear which utility functions should be included in the aggregation. Should every agent that does or ever will exist have their utility function included? If so, then the aggregation would indicate that humans should be replaced with large numbers of agents whose preferences are easier to satisfy1 (this is true even for average utilitarianism, because there needs to be enough of these agents to drown out the difficult-to-satisfy human preferences in the aggregation). Should the aggregation be dynamic with the population, so that at time t, the preferences of agents who exist at time t are taken into account? That would be dynamically inconsistent. In a population of sadists who want to torture people (but only people who don't want to be tortured), the aggregation would indicate that they should create some people and then torture them. But then once the new people are created, the aggregation would take their preferences into account and indicate that they should not be tortured.
I suggest a variant that I'm tentatively calling current-population utilitarianism: Aggregate the preferences of the people who are alive right now, and then leave this aggregated utility function fixed even as the population and their preferences change. By “right now”, I don't mean June 17, 2014 at 10:26 pm GMT; I mean the late pre-singularity era as a whole. Why? Because this is when the people who have the power to affect the creation of the AGI that we will want to maximize said aggregated utility function live. If it were just up to me, I would program an AGI to maximize my own utility function2, but one person cannot do that on their own, and I don't expect I'd be able to get very many other people to go along with that. But all the people who will be contributing to an FAI project, and everyone whose support they can seek, all live in the near-present. No one else can support or undermine an FAI project, so why make any sacrifices for them for any reason other than that you (or someone who can support or undermine you) care about them (in which case their preferences will show up in the aggregation through your utility function)? Now I'll address some anticipated objections.
Objection: Doesn't that mean that people created post-singularity will be discriminated against?
Answer: To the extent that you want people created post-singularity not to be discriminated against, this will be included in your utility function.
Objection: What about social progress? Cultural values change over time, and only taking into account the preferences of people alive now would force cultural values to stagnate.
Answer: To the extent that you want cultural values to be able to drift, this will be included in your utility function.
Objection: What if my utility function changes in the future?
Answer: To the extent that you want your future utility function to be satisfied, this will be included in your utility function.
Objection: Poor third-worlders also cannot support or undermine an FAI project. Why include them but not people created post-singularity?
Answer: Getting public support requires some degree of political correctness. If we tried to rally people around the cause of creating a superintelligence that will maximize the preferences of rich first-worlders, I don't think that would go over very well.
1 One utility function being easier to satisfy than another doesn't actually mean anything without some way of normalizing the utility function, but since aggregations require somehow normalizing the utility functions anyway, I'll ignore that problem.
2 This is not a proclamation of extreme selfishness. I'm still talking about my decision-theoretic utility function, which is defined, roughly speaking, as what I would maximize if I had godlike powers, and is at least somewhat altruistic.