LogFAQs > #966134570

As someone who knows far too much about both characters, Donkey Kong.

To base the characters on titles where they appear together:
-Bowser is generally a little stronger than DK (Bowser's usually max strength, DK is usually slightly underneath him). However, Bowser is almost always slower as well.
-In Mario Party 5, Donkey Kong shows up and punches Bowser in the nose sometimes if you land on a Bowser Space. Bowser will react in fear and run away after stealing 10 coins. This is the only time one has ever showed fear to the other. It is likely, in a close-quarters match, Bowser believes that he will lose.
-In Mario Party DS, Bowser shrinks everyone down to tiny size, except Donkey Kong, who he turns into a stone statue. Once DK has recovered, he runs into Bowser's Castle and beats Bowser on accident, as he was just storming it INTENDING to help, not actually knowing where Bowser was.

But if you want to discount goofy Mario Party plots (which... y'know. Is probably better for your health), I think it just comes down to a personality issue. Bowser has a significantly better AoE presence, but he's both insanely prideful and an incredible showboat. DK is single-minded when he's not goofing off, and "winning a fight, especially against a king" is probably second only to "all my bananas gone" for him. DK is GREAT at capitalizing on mistakes, and Bowser is great at getting upset and making them when he's not dominating immediately, and DK should be able to match his strength.

tl;dr, man I wish more people played Jungle Beat, DK's baseline respect would be so much higher.

https://youtu.be/10qXU4DVED8