Early on Mutt ranked near the top on my "worst figures" list but upon finding one that was very nicely painted, I found that a good paint job really brought out the details and made the figure pop, so he actually rose through the ranks so far as to become one of my favorites in the line (I'm hoping I like his on-screen character as much).
I would have to cast my vote for the Ugha warrior. He looks more cartoonish than the other figures and lacks a certain amount of detail (what detail he does have isn't very sharp), and doesn't look a whole lot like his on-screen counterparts. This is a figure that could have used a good paint wash and a few extra colors (the blue used on the cardback photo would have been a nice touch, I think). Let me clarify by saying that the Ugha warrior is not a bad figure by any means, but it's probably my least favorite of the bunch.