What? How is this even a question?

Demi-god (or god, really, as he's certainly more powerful than other Maiar as presented) with entire nations at his direct beck-and-call, versus a guy with a wand, some sidekicks, and more phylacteries than is good for him.

Sauron, corporeal, just beats the **** out of him. Incorporeal, he mobs him with 10 million orcs. Seriously, what the hell is Voldy going to do? Even if Sauron dies, he's immortal unless someone chucks the One Ring into Mount Doom. Voldy, admittedly, has more phylacteries, but they are far more vulnerable.