I am used to the current world and not completely immune to status quo bias, so I am not sure. But as far as I can imagine a choice in which maintaining current friends and relatives wasn't at stake, the optimum would be a world where my overall mental capacities would ensure my being part of the global intellectual elite; that would certainly require the global IQ average lower than today (not sure how much), if my brain had to remain unchanged.

Edit: all that holds ceteris paribus; if I had the option to gain status otherwise, e.g. by inheriting an awful lot of money, I'd prefer that to acquiring status by intelectual superiority over others.