QQ in the vast majority of siutations overall but there are occasions where I find AK easier to play in cash games. I'm still a beginner, so my logic might not be 100% correct.
With AK it's advantageous to see all 5 cards. If I 3 bet, and am then 4 bet I don't like calling. They potentially have QQ, JJ or 10 10 as well as the other obvious
hands. If I call and miss the flop what do I do? It's easier for me to rip it all in, or to fold if I think I'm up against someone who only 4 bets AA and KK. Only 2 options to choose from can streamline my thinking and I might prefer AK in those spots.
I might also move all in vs a 3 bet with 1 to 2 callers at times too. The player(s) who called the 3 bet didn't 4 bet so I'm thinking they probably don't have AA or KK. The player who originally 3 bet still could so that's a risk. With the dead money in the pot it could be worth it to get it all in.
Assuming 100 BB effective stacks. 1.5BB in the pot from the blinds. I raise to 2.5BBs, it's 3 bet to 7.5BB, one cold caller. 19 BBs in the pot by the time the action comes back to me. If I move all in with AK for 97.5BBs and get one caller holding a pair other than AA or KK, I've put my remaining 97.5 BBs in to potentially take down a 214 BB pot I'd need 45% equity to make it worth it. With AK suited I'm just about there vs QQ or a lower pair, with AK off-suit I'm not quite. I have added fold equity though, and I'd be taking down the pot pre-flop at least a certain percentage of the time.
Something to also consider if I am called by one player holding QQ, JJ, 10 10 etc. in that situation is that the player I folded out might well have held one of my outs. He could easily have 3 bet, or called a 3 bet with AJ, AQ, KQ, KJ suited etc.
QQ I can see more flops with, and proceed from there in certain spots. That flexibility is nice to have at times, but can make me feel uncertain in my decision making on occasion. In that same 3 bet pot +1 caller scenario from above do I 4 bet to around 30 BBs, move all in, or call, facing 2 players post flop? It's an extra decision to potentially get wrong. Post-flop position comes into play as well. With more experience I'm sure I won't worry so much.
Generally though it has to be QQ, especially heads up or against each other of course!