Gandalf, without a doubt.
I mean seriously, it's friggin Gandalf, and Gandalf is awesome.
However there are very few characters I don't like(so few in fact that I currently cannot think of any).
The Fellowship itself, including Boromir is just awesome.
Funny that I noticed this thread just now, maybe 10 minutes after deciding that I'm going to watch the trilogy again and soon. In 1080p. The extended editions. Yes, I am excited.
I've seen all three films more than 4 times each, and I still want to watch all of 'em again.
I seriously cannot wait.