If you're talking about tournaments, it depends on where you are in the tourney.
At the beginning, don't go 'all-in'. I've found that the beginnings of tournaments, especially at the lower level are 'all-in' fests, and you could put yourself out very early, because someone will get lucky.
As the tournament continues, you need to take notes of the other players, and their style of play.
Are you in against someone who plays many hands, or few hands; never folds, frequently folds; continually raises, or continually calls.
You have to make a judgement, just not on the cards you have, but on the habits of your opponents.
So, as the tournament goes on....watch, and act carefully.
I tend to go all in with AA slow play usually loses to either 3 of kind to someone also calling with a pair and hitting their nominated. or 2 pair usually high cards but go with your gut.
Never 2nd guess yourself.
If there is someone continually raising and I get a great set like that, I'll check and let them step into the trap.
All too often, I get AA make a raise and everyone folds.
So, it depends too on what style of player you are, and what appearance you have been giving off.
I've even folded aces before in a tourney ...as everyone is going all in and I'm one click away from a higher tiered prize. It was the right move in THAT situation.
Different circumstances require different actions. how far are you in a tournament and how are the other players playing at the table. what place do you have at the table, stack size. You can play the same pair differently, and because you can't predict how a hand will run, you can't actually say in advance how to play a hand. But playing slowly would give the opponent more time to assemble something and most of the time they can do it. And then you find yourself on the river instead of at the very front at the very back because AA is the strongest hand preflop but in the end it is only 1 pair against set street or flush or simply 2 pair loses
Situation is everything and it seems as it almost every guideline in poker has its exceptions. With this said, AA is a premium hand preflop (best possible hand at that point) and you should usually do best with standard open-raising and value betting/re-raising when appropriate; sometimes this will mean All-In and other times it won't.
Slowplaying (sometimes called "trapping") is a risky strategy which shouldn't be the default (although some micro stakes players seem to ONLY slowplay Aces). One time when slowplaying makes some sense is when you are facing an aggressive (often times megalomaniac playstyle playing a wide range of hands preflop) playstyle and know that they will be doing the betting for you. In this case, they are likely to interpret your checking as weakness (but it isn't, you have Aces!) and they will bet for you and you simply call consistently with an options re-raise by you on the River for extra value.
If the opponent isn't likely to keep aggressively betting when they don't have much (why slowplaying isn't the default against every playstyle), then you are typically best value betting and building the pot yourself.
At a higher level (doesn't necessarily need to be the pro/high stakes level of poker, but at least higher than freerolls and the smallest of microstakes), it becomes less and less profitable to slowplay 100% of the time, but being capable of trapping occasionally is a dangerous threat for opponents to face.
It depends on which stage of tournament is. Personally if it's early stage of tournament i usually play all in preflop. If it's later stage of tournament i play different strategy depends on many variables.
I play aces very simply! In the beginning I try to avoid multipot by doing 3 betas and 4 betas! And left alone, I play bet bet bet, but if I don't strengthen, then I will fold against a raise from a tight player!