Ok, after actually thinking about this for 5 minutes, it's ludicrously obviously that the falsehood is the correct choice, and it's downright scary how long it took me to realize this and how many in the comments seems to still not realize it.

Some tools falsehoods have for not being so bad:

• sheer chaos theoretical outcome pumping. aka "you bash your face into the keyboard randomly believing a pie will appear and it programs a friendly AI" or the lottery example mentioned in other comments.

• any damage is bonded by being able to be obviously insane enough that it wont spread, or even cause you to commit suicide you don't believe it very long if you really think believing any falsehood is THAT bad.

• even if you ONLY value the truth, it could give you "all the statements in this list are true:" followed by a list of 99 true statements you are currently wrong about, and one inconsequential false one.

Some tools truths have for being bad:

• sheer chaos theoretical outcome pumping. aka "you run to the computer to type in the code for the FAI you just learnt, but fall down some stairs and die, and the wind currents cause a tornado that kills Eliezer and then runs through a scrapyard assembling a maximally malevolent UFAI"

• perceptual basilisks, aka "what Cthulhu face looks like"

• Roko-type basilisks

• borderline lies-by-commission/not mentioning side effects. "The free energy device does work, but also happens to make the sun blow up"

Note that both these lists are long enough, and the items unconnected enough, that there almost certainly many more points each at least as good as these that I haven't though of, and that both the lie and the true that likely to be using ALL these tools at the same time, in much more powerful ways than we can think of.