Emerald, most definately. Most of my, actually all of my Pokemon are on Emerald, yes and that's where I made the most progress, and when D/P comes out, I guess I'll have to trade em over to them new games, heh.
I voted for Emerald because it has the phone, and the Pokemon characters move. The Battle Frontier is the best kind of entertainment for people who already beat the Pokemon League. I love it there!