Which Golden Sun game is your favorite?
I'm going to have to go with the Lost Age. It's world was much more detailed and had much more content then Golden Sun, which I always felt was incomplete (although, Camelot practically forces you to play the sequel with the cliffhanger ending). I also believe it has the superior soundtrack, Sakuraba rules, etc.
My only gripe about the game would have to be the Transfer feature. Not everyone has two Gameboy Advances and a GBA link cable. So this leaves most people to input a six-page password to transfer the Clear Data information from the first Golden Sun, which isn't very fun.
Still, I love both games, and would be very happy if Camelot ever makes a third game (it'd be perfect with for the Nintendo DS).