Hmm to be quite honest, running the list of Sinnoh Pokemon through my head I can't see one that I'd like to get rid of, but if I had to make a decision it would definitely be Burmy. I can see Game Freak trying to think of something creative and it's concept was interesting but, it's design was rubbish. I think that's an unintentional pun right there but yeah to get to the point Burmy overall is absolutely awful. It's stats are awful, the overall design isn't particularly great and there's nothing much I personally like about it.
Also Combee is the cutest Pokemon in existence. :(