Roxie's! I laughed so hard when I realized what I was listening to...it was actually the only one I really noticed was different until it was pointed out, actually. What I especially liked about it was how the trainers would stop singing after you beat them; that was quite clever. I prefer the English language version to the Japanese version, though.
Although listening to that video, Elesa's is quite catchy as well, in a weird sort of way. Burgh's is just creepy, it'd be more suited to a ghost-type Gym than a bug-type one...