It’s difficult to say as the two Sith Lords were around at different times. However, it’s fun to assume a few things for an interesting argument. Revan was both the most powerful Sith and Jedi in his time, and there wasn’t much he couldn’t do. Malgus, on the other hand, was only a Sith Lord serving others in the Sith Empire. He never opposed the Sith higher-ups as much as Revan would. While Malgus was incredibly strong, I don’t think he’d be able to beat Revan. Malgus’ anger and rage would help him in a fight, but it would ultimately lead to his downfall. Since Revan has mastery of both the Light and Dark Side, he’s much more balanced and discerning. I’d like to think he’d be able to read Malgus’ moves and counter them suitably.