It's funny; My feelings about the first three movies correspond to their chronological order. I really loved Raiders, and while I also loved Temple (Which took place one year before Raiders), I loved Raiders more. Then Last Crusade came out and I loved that one more than the other two combined.
My favorite moments from each are the scene Belloq is lecturing Indie on how they're not so different in the first, the scene where Indie cuts the rope bridge in the second, and the fight on the tank in the third.
Of course, Crystal Skull throws this all out of whack by being the latest and yet the one that I just like, rather than love like the other three. Ah well, maybe when they make a fifth that's even worse we'll all appreciate the fourth better.