[johnc]

I lean towards raising because of the huge pf equity AA has. My approach is to look each street having unique equity opportunities - and exploit those opportunities as in the best way possible. If my equity at any particular street is not huge (such as with small pps) but could improve to be very big (hitting my set with my small pp) then it to my advantage to "limp" or invest a little with the potential to win alot. With AA, pf this is not the case. Pf equity is far too big to pass up a raise, IMO. If you get even luckier and hit your set (and 1 or 2 see the flop), in a tight game you'll be thankful that you able to extract those bets pf due to the fact that only 1 ace remains unseen making it unlikely your 1 or 2 opponents has it. They fold, or you try a slowplay to a bigger street, where they fold to your bet.
The only occassion where I see a benefit to limping is if your opponents are highly skilled and very observant - making the deception value of your rare limp +EV.