It's easy to fold small-mid pairs against a 2b-4b if:It's hard to fold preflop holding any pairs against 2BET-4Bet knowing that the chances of hitting a set is a huge advantage.
the possibility is the same.
but I think AA is having the lowest chance, because AA will go against of the big Ace like AK, AQ it reduce the chance of hitting a set.
the higher the number of outs on the flop greater the chance of win , here are some suggestions in the PokerStars poker school
good luck in poker and in life