I've yet to play against a Charizard, Falco, Meta Knight, or Palutena.
I seldom see Pit, Samus, Toon Link, Wario, Luigi, DK, Peach, or WFT.
In direct response to the OP, Yoshi and Sonic are both very common mains, so if you want to pick a character others don't use they're both bad picks. And the people telling you Diddy Kong clearly haven't played in (m)any tournaments, because he's rampant in competitive play.
That being said, why not just play the characters you're comfortable with?
On a side note, I personally find it very satisfying that nobody plays Meta Knight.