this thread didn't turn out as well as i had planned, i dont think i explained myself clearly enough in the first place.
the point i was trying to make was, depending on the range of your opponent, the hand which is better actually changes. i discovered this whilst mucking around with pokerstove today, and (nerd alert) i found it fascinating.
here are the results i came up with

- range1.jpg (61.29 KiB) Viewed 597 times
zooming in a little bit gives

- range2.jpg (59.06 KiB) Viewed 597 times
so in summary, if the villains range is:
AA: we should choose 88
AA and KK: we should choose AJ
QQ+ and AKs: we should choose 88 - this is becasue 88 is better against AK.
ranges of between 5 and 10% = they are pretty much exactly equal. this is very interesting, because it shows that these hands play very similarly against a typical 3bet range of a good player.
now it gets interesting. for ranges of between 10 and 50 odd percent, AJ is actually better than 88. i think this is because there are lots of hands like lower AX and Jx type hands in this part of the range that AJ dominates, but all of these hands still flip with 88.
then after about 50% of hands, 88 begins to win again, and this would mostly be because of the double undercard type hands that 88 crushes.
an important point however is this doesnt take into account things like the fact that an ace high flop is scary for 99-KK, and that there are more reverse implied odds scenarios with AJ, and 88 often has great implied odds. so in a poker game where there are other strategies that need to be taken into account, 88 is better.
i think i need to word the question more carefully next time though