1) I'd say Bowser is stronger than Donkey Kong overall, having magic, fire breath, insane strenght and resistance, plus being really fast and being able to use his Koopa Shell. Thag said, Donkey Kong is the more likely one to win. Despite Bowser's advantages, I think they're an equal match.
2)Mario. He's more skilled and controlled than Luigi on his jumps, has more experience to his name and is quite simply more confident in his abilities.
3) Diddy Kong. Not praising Diddy's intellect, but Donkey is just plain dumber.
4) Actually, neither are that evil, but if you look at facts, Bowser Jr. Can be more evil than Bowser. He'll do anything to please his dad, after all. Think about it for a moment and consider that he ruined a bunch of island's worth of lives just to frame Mario.