Find your niche.
I'll go with Palkia. I just don't like it. I'm a bit biased, having played Diamond over Pearl, but I really think its design, concept and typing could have been better. It's ironic, too, because I absolutely love Water-types. And as for how it fits the thread title, even though the thread title isn't the question, Palkia can be overpowered at times, having only a single weakness, unresisted STAB, high Special Attack and good bulk. But come to think of it, I also hate Regigigas a lot, because Slow Start is absolutely horrible, and it's not as original an idea as I'd like legendary Pokémon to be. Regigigas is an obvious choice, though, so apart from him, Palkia's my least favourite.