The first UA, definately. It had better action, more Hulk, Millar/Hitch homages, and a more theatrical feel. UA 2, while not as bad as some people think, suffered greatly from 100% deviation from the comic, especially in the action dept. They couldn't pace a fight worth a damn without at least a Millar/Hitch bit to start off like with Hulk. Plus, while Black Panther was cool, seen one jungle, seen 'em all.
Thor got more airtime in UA 2, but I still like the first better. Every time.
IMO, INVINCIBLE IRON MAN was actually more mediocre to me than UA 2, and THE AMAZING SCREW ON HEAD blew them both out of the water despite being maybe 1/4th the length (I bought the DVD last night; hilarious!).