While Cavendish is an extremely talented sprinter, I don't think he's such a great ambassador for the sport. He often throws temper tantrums in his races (at least, races that I saw on vs), and I saw him be very snotty with a race official before his start at the Tour of CA prologue.
Well he IS a sprinter! I didn't know he's acted badly, that's too bad, but, honestly, what bike racer at that level behaves like an adult on a regular basis? I guess I was going by what I had heard about his work ethic, his approach to team work, that kind of thing, plus he was very gracious during interviews during the T de F which is where I saw him the most.

At least I didn't nominate Ricardo Ricco for Ambassador!