Poll
63%
38%
Obi-Wan's likely reasonably faster and more skilled, while Malgus is stronger, is much more powerful, and has greater endurance and durability.
A battle like this could really go either way, to be entirely honest, but I would think that Malgus would be more likely to pull through simply because the sucker is impossible to put down.
Now, if we're being inclusive of Malgus's "Oneness" amplification, he should have a reasonable edge over Kenobi.
I'll give you skill, but I wouldn't say that Kenobi's faster. Malgus was able to keep up with Aryn Leneer, and she was pretty damn fast:
"Aryn did not bother to respond. She dwelled in the Force, floated in and on the warm network of lines that connected all things, one to another. Her consciousness expanded to see and feel everything near her. She focused on her perception of the passage of time, first on how it felt as she moved through it, then on spreading it, stretching it, until she could linger in a millisecond as if it were a moment, then a minute. To Zeerid it would appear that she were a blur of motion, existing simultaneously in multiple places. To her, it felt as if the universe around her had stilled. She smiled, seeing the moments that hung before her, each millisecond a long moment in which she could think, in which she could act. The effort taxed her, and she knew she could not maintain it for long."
And he got more powerful after that too. Though Malgus would simply own Kenobi with the Force.