No counterspelling in HP? Fine, call it blocking (which HP has out the gills) and Sauron's golden. I was using counterspell to describe what he does at Numeneor, but blocking may in fact be more accurate anyway. Semantics don't interest me here, what interests me are abilities and we know that Sauron is very good at defeating magic. Voldemort uses magic, Sauron defeats magic. Its really that simple.

And I just reread the section of Two Towers where Gandalf describes his battle with the Balrog. Nowhere did I see a reference to this death and resurection of which you speak. He was very weakened yes, but that's a long way from death though. He does not even say "I was sent back" or anything like that. The closest he gets is "I felt life in me again", but that's still different from dying and could mean any number of things besides "I was dead". Of course he is also described as being transparent at this point, until he is healed in Lothlorien, but that's still not killed, dead or died, just unusally unrefractive.
Now if fighting a flaming demon nearly as old as the world on the top of a freezing mountain above the clouds in a battle that caused thunder, lightening and fire visable "from afar", after falling to the uttermost foundations of stone, then climbing back up, fighting all the way, doesn't kill a spirit forced to wear the body of an old man, I don't see how AK can effect a being of vastly greater power such as Sauron.

At this point I rest my case, spirits such as the Maiar cannot die or be killed. AK kills stuff that can be killed, if not it doesn't work. Sauron is a Maiar, hence he cannot be killed or die so AK does not work on him.

And nowhere have I claimed that Sauron is immune to all magic, or is a walking AMF, merely that he is immune to certain spells based on what he is and is freakishly good at blocking magic, hence using magic against him is a strategy doomed to failure.

Conclusion: Sauron can defeat magic makes Hydrogen bombs look cute bunny rabbits with mild indigestion through some means, the exact details of which should be irrelevant. Sauron is uneffected by things that kill their target, since he cannot be killed. Voldemort is entirely dependant on magic, which Sauron can shut down. Hence Sauron wins.