Ultimate Fantastic Four wins hands down. It hit the nail on the head with how the Fantastic Four should be written: great humor, great action, and killer interaction between the kids. It did a damn fine job telling a stand-alone story that someone unfamiliar with the book can jump into, but that also ties back into the group's mythology. And it brought back Mole Man. Dig it, folks.
USM and UXM are tied distantly at second place. They were both important footnotes in their respective storylines, but they were executed a little clunkily. Bendis threw too many characters in the story for no real reason, kllled off a plot thread before he let it develop, and wasted another potential Ultimization. Motivations felt rushed in an attempt to get to the end point. UXM was enjoyable, and got the characters pretty well, but it just seemed to come out of nowhere

and I'm worried we won't be seeing any more Dazzler now.
The Ultimates was just coplete garbage. That Annual was so bad. There wasn't a single good thing about it.