I exhaustively simulated (every possibility is run) AA vs any pocket pair and AA vs any suited connector. Firstly let's cover the pocket pairs:
Obviously it is best for the under-pair to have different suits, in order to win with flushes. The best pocket pair to have is pocket eights. This is because all straight possibilities will result in a win. This is also the case with sixes and sevens (aces are blocked with pocket fives), but it is important to have a higher pocket pair, since you won't get counterfeit as often when you hit a set. For example with pocket sixes on 6777x results in a loss, while with pocket eights on 8777x results in a win. When we run the odds we get the following: 8s8c (20.20%) vs AhAd (79.80%).
Now on to the suited connectors. I didn't even bother to run suited one gappers, since they make less straights and therefore are for sure a bigger dog against aces. The suited connectors that make the most amount of straights are 56-JT. It is important that the hands' suits are different then both aces, since when the flush is made on flop or turn, the aces will not have (extra) outs. Let's make an overview of their equities against aces:
JT's equity is the lowest, since his straight outs are blocked by the aces and even when broadway is hit the board has to run out unpaired.
T9's equity isn't the best, since the board can run out KQJT, giving aces a better straight.
98's equity isn't best, since the board can still run out KQJT.
Now our last 3 hands are extremely close in equity. All the straight that can be made will result in a win. The equities differ however. Let me explain:
With 65, A234 and A2345 are blocked by aces. With 76, A2345 is blocked by aces. This explains the fact that 87 has more wins than 76 and 76 has more wins than 65. One would expect 87 to have the highest equity and 65 the lowest, but this isn't the case. The reason for this is the amount of ties each hand makes.
The boards A2345-89TJQ, will generally result in a tie. See this image for a nice overview of all possible 'straight boards'. The key is the A2345 straight combination. This straight will happen way less frequently compared to the other straights, because it is blocked by aces.
Essentially the goal is to have the most amount of straight ties. When 65 blocks A2345 obviously some of those ties vanish, but it's better to block A2345 compared to other straights. This is because when a straight is blocked it will occur less, relative to the amount of which it occurs. If A2345 occurs less, you will ultimately lose less absolute straight ties, compared to when another straight board is blocked. As can be seen on the picture 65 is the only hand that blocks A2345, which results in 65 having the most amount of ties.
Now let's explain the difference of the amount of ties between 87 and 76. 76 wins on A2345 and 23456. On all other boards 76 will tie. 87 wins on 23456 and 34567. On all other boards 87 will tie. Here you can see that 76 has more ties, since the six boards 76 ties on is not blocked by aces.
I exlplained that 87 has the most wins followed by 76 and then 65. However, this difference in wins is relatively unimportant compared to the difference in amount of ties between the three hands. 65 has by far the most amount of ties, followed by 76 and then 78. Therefore 65 has the best equity, then 76 and then 87.