The personality Ash's Gliscor displays makes it fit Ash; it does what it does better than Bayleef and Aipom ever hoped to.
As a species in their entirety, I will agree with the opinion of the masses and say Gliscor doesn't fit Ash; it fits Paul better than it does Ash (though we haven't seen Paul's Gliscor do much of anything...I'd personally like to see a rematch, because Ash's Gliscor is at a point where it could probably tear Paul's Gliscor apart. =])
I've said it many times; Buizel annoys the living piss out of me.
The next best candidate is Noctowl because of its misuse. Of all the shiny species to catch, he bags this eyesore, uses it in one gym, and has it do nothing else but glow the entire Johto arc. Honestly, what a gigantic waste. :|