The Snivy line in general because I was so hyped for them before the games came out and it turned out to be the worst starter I've ever played with. Even Chikorita was more usable than this thing and Chikorita had almost every gym and Elite Four working against it. To me, the fact that it may get Contrary at some point isn't enough to make up for its pre-Contrary awfulness. I also hate when people say Serperior's a better pokemon than Emboar and Samurott purely based on looks.
No, Emboar is the worst, ANOTHER Fire/Fighting with no excell in stats minus attack which is ok for his moves. And learns close to no useable type diversity. Everything Emboar does Infernape and Balziken did first and better.
At least serperior looks cool, has moves that compliment its stats and with the move tutors in Black and White 2 it gains a large number of type diverse moves that fit it well