I'm going to betray my favorite character class (spaz) and vote for jazz on this one. Though my reasons for doing so are more to even it out than picking my 'favorite character'. So I broke the most obvious rule in the topic...

I feel that it's the way most levels are designed that make it hard for jazz's abilites to really shine as Odin stated. More emphasis on jumping than actually moving through free space which Jazz's Heli ear could be really awesome for that purpose alone. Jazz could potentially have a slight advantage in more vertical levels due to the uppercut attack but there are so few of theese type of levels.