I for myself can sincerely not find a common ground to the magic of these two opponents...if there was to be a common ground, made up of, say, half the powers/spells/immunities/tactics of one and half of the other, I feel Sauron would win, if nothing else because the 2 characters are simply of different "scope"..one a godlike eternal spirit, the other a moronic crackpot (I know, I know, just let me have some fun )....and half a ton is more than half a kilo.
and even if this was possible, I can simply not immagine how this common ground would be "shaped", by what rules and limitations, or absence thereof.
wherefore I think the game is off.

the only confrontation I can somehow figure relies mostly on the analysis of the characters, their behaviour, their "psyche"..their motivation and ambition, the impact they make on the books where they are present, and on the characters therein.
of course this is even more debatable and subjective and it goes a lot about the literary taste of the reader. in my case this is, once again a hands-down victory for Sauron...if nothing else, because of the literary value of tolkien as opposed to Rowlings. the former intended to create from scratch an epic saga and tradition for a nation that had no such thing..the latter simply wanted to write things that she liked and has capitalized on the resulting boom. nothing wrong with that, and I've read the books with pleasure, but in my opinion it's somehow "less of an achievement" than that of Tolkien

all of the above are purely opinions and totaly debatable...don't shoot the pianist