Wow, of course I'd main Diddy over DK, but I like both
IMO Diddy is better, but I never played the game so I'm not so sure about that.
DK was really fun to use in Melee. I love his fair, but now since you can't LCancel it anymore it's really risky and worse... I like DKs power and playing style.
What I've seen from Diddy is that his bananas will have a pretty big role in his game. It's awesome how you can always use them and fire at your opponents. They're maybe even better than Peach's turnips... Diddy is really fast and also looks fun to play.
Personally I'm sure I'll play both a lot, but Diddy more, because DKC2 was such an awesome game and since that game I really love Diddy.