Ace King

Ace-King, especially suited, is nice because it plays well against almost any hand.  You're also likely to win big pots when you win.  The ideal hands for you to get up against are AQ, AJ, AT, KQ, KJ, etc. which you dominate.  The only hands you fear are AA and KK.  All other pocket pairs are under-pairs, so you have about a 50/50 chance against them.  In fact, it's even better than 50/50 in terms of EV, because you generally know for sure when you're winning (there's an A or K on the board), but they can't be sure their pocket pair is good if there are any cards on the board above their pair.  So, for example, if they have 88 and the board comes AT3 , you're winning and you can be pretty confident about it.  If they have 88 and the board comes QT3, they're winning, but they can't know it for sure, and a semi-bluff by you may even make them fold the best hand.

You generally don't want to limp with AK.  Many people think "why should I raise preflop with AK, let me see a flop and see if an A or K comes before I started trying to get money in".  This is wrong for a lot of reasons.  First of all, you're playing AK to make just a pair.  Of course you're happy when you make two-pair or trips or a straight or something like that, but you can make those with any hand.  Two pair with a T7 is almost as good as two pair with AK.  The nice thing about AK is that all you have to do is make a pair, and it's usually winning.  Second of all, you want to get money in the pot when people are behind you.  If you see a flop and an A comes, people with bad hands like QJ or KJ will probably fold to a bet, so you can't get their money.  If you raise pre-flop, they are more likely to call, so that you get their money.  If someone does call on the flop, you're more likely to be beat (when you have just a pair), especially if you allowed a lot of people to limp.  Third, by raising you reduce the set of hands you're likely to be facing, so that you are in a more known position.  Best of all, a lot of the hands that will call you are AQ,AJ, etc. which you dominate.

One flop to beware of is something like QJ or JT or QT.  You might think that you have two overcards and a gut-shot straight draw, which is a good set of outs, but those outs are no good.  Your overcards will frequently be making straights or two-pairs for your opponent, so you're simply drawing to a big beat.