I don't think I would choose to erase any Pokemon. There are some out there that I dislike, but even the least popular Pokemon have people who consider them their favorite. It wouldn't seem right to erase any.
But... I guess if I absolutely had to do it, I'd go with Toucannon. I strongly dislike its design. It lacks any creativity in its appearance, in my opinion. Just looks like a regular toucan! Toucans are super cool animals and deserved something more interesting.