1.Malgus wins. I think Malgus is overrated and shit though....
2.Malak takes this, no doubt. He was powered by a whole race of force sensitives and 8Jedi. He would choke Malgus out.
I'm not going to bother with 1, since at that point Malak is such an unknown that there's nothing to go off of except accolades of himself as a Jedi, which don't gauge his ability as a Sith.
2, however, is an interesting fight. Force-Wise, they're actually really similar. Malak has force-choked two Jedi Knights at once, killed one with a lightsaber throw and the other with a blast of Force Lightning. Malgus has easily Force Choked a Jedi while not even paying attention to his presence, and has killed multiple Jedi at once with Force Lightning. Saber-Wise, there isn't much to go on about Malak, but as as Jedi he was amongst the best swordsmen of his time, and as a Sith he was apparently second only to Revan. Still, does this put him above Malgus? Dunno.
This sourcebook: The Jedi Path: A Manual for Students of the Force regarded Malak and Revan as GREATEST CHAMPIONS of the Order in its history.
Aboard Leviathan, Malak fought against the trio of Revan, Bastilla and Carth singlehandedly and managed to subdue Bastilla, forcing the others to retreat. By this time, Malak claimed to be a match for (Darth) Revan.
Duron Qel-Droma had visions about Malak and he regarded him as extraordinarily powerful Sith Lord. Even Plagueis would give examples of Malak and Revan to Sidious while lecturing him about ground realities of the Force.
Malak did manage to run a whole Sith Empire effectively after fall of (Darth) Revan, which is phenomenal accomplishment for a single individual.