If I recall correctly, Mario is dead even.
Mario once
Peach
Yoshi
Donkey Kong
Mario once
Luigi
Bowser
Wario
Don't think I'm missing any if that's the case.
Thankfully, most other Mario MUs that are even likely are largely Mario Ws
K. Rool beats Blackbeard and Ridley
Rosalina is going to shit on Palutena as much as I dislike that MU. My preferred for Rosalina may even have her lose also since I like Celestia for her. But they'd go with Palu.
Jr. Is paired against WAYYY weaker verses so he stomps often.
Bowser will likely beat Eggman of that MU happens much to some people's dismay. He also beats Lord Hater I guess.
Waluigi beats Robbie Rotten. I think that's his most popular.
Dimentio wins a few of his I think aside from Enerjak but that's fallen off lately in favor of just better opponents for both. He's definitely got the more debatable MUs and even though it's outside help and definitely not standard they will probably give him Super Dimentio I feel like. For reference his MUs are Marx, Magolor, Solaris, Flowey, and I forget the name but some dude from drawn to life. I shudder the thought of every single one of these fights if I'm honest.
Toad wins most of his MUs not like many are that great to begin with.
King Boo beats all of his likely opponents iirc
So yeah, things are looking good for Mario's record in DB.