Well, according to
SportIllustrated/CNN.com the title holder is....the Cincinatti Bengals!!!!

What surprises me is how many hockey teams made the list, when I think they're all pretty much the same design. In the NFL I'd say Browns are actually worse than Cincy. Same with Miami and Oakland. All the Raiders have going for them is a good color scheme.
For MLB, why does a team called the Angels use red as their primary color? A color associated with a devil?
For the NBA, it's gotta be the Nuggets.
But yeah, the Bengals uniforms is a bit hard on the eyes....