Favorite: Sceptile. He looks so cool and I like the "king of the forest" idea, and he's pretty good too.
Least favorite: Definitely Charizard because he's overrated(3% raw usage in OU!!!!!) and sucks horribly competitively thanks to its weakness to Stealth Rock, common weaknesses, Solar Power making it even more sensible in the sun, and Politoed and Tyranitar. I'm pretty sure Mega forms are going to be banned in OU so Charizard is still gonna be horrible.