Best: Toad (the one Toad, not the entire race). He may not be the best jumper, but he's got more than enough speed and strength to make up for it, and he's always willing to help out the Bros time and again when help is needed. An honorable mention goes to the Hammer Bro from MP8. WHile his voice was kind of annoying (listen to him taunt), it is great to see classic playable characters like him in instead of abominations like Petey Pirahna (let us hope he is never playable in MP).
Worst: While they are not neccesarily the worst, I have to collectivley say the baby characters. I don't like that baby characters appear in the same game as adult characters (except for when the story calls for it, like PiT). If we wanted to play as Mario, we would use Mario, not baby Mario, you know. If I can't vote for all of the baby characters, then just put baby Daisy in that spot for me (quiet unneccesary). A horrible mention goes to Blooper's appearance in MP8. While it is great to see classic playable characters like that, I sort of thought Blooper was kind of a stupid choice. I don't know why, but I felt rather silly playing as him after unlocking him. On the upside, at least it wasn't Petey..
Nominee: Can I vote for both 2D and Mario Sports? If not, just Sports.