The worst internet forums I've seen are:
- Yahoo answers (if it counts)
- RP forums in fanfiction.net
I'd say Bulbagarden is the worst mainly because the staff is corrupt as ****. They take advantage of their positions to ban whoever believes in God and has an opinion that differs from their own.
They also use it as an online political recruitment center. By this, I mean that they support the causes of certain users, let them violate the rules without getting infracted, and in return the bulbagarden staff members think they'll get rewarded with votes for their political party.
So in other words, they're a pack of fascists who take advantage of a Pokemon forum to punish those they disagree with and gain new political supporters.
Overall, I'd say that has some of the worst staff members a Pokemon website has ever seen.