*rereads thread while model runs on computer*
*realizes that while he commented from the sidelines, he never actually weighed in*
Well, firstly, I'd like to say that this is a much more reasonable question than the "Gandalf v. Dumbledore" or "Gandalf/Sauron/Saruman v. Voldemort" type questions: the magic-users of Tolkien's world if not elves were generally incarnate nature spirits, cf. Gandalf the Grey and Gandalf the White--they didn't so much die as go away and decide whether or not they wanted to come back/be sent back. (Sauron and Saruman had both fallen... there were no dark Valar to reincarnate them (even if that were how it works) b/c... Morgoth and that whole Silmarillion thing...). Here both characters are mortal and their essential types under all their trappings of evil and power are the same.
Also, one last thing: Voldemort needs his wand to use magic, but Vader doesn't need his lightsaber to use the Force; it's just handy to have. So if the fight ever got to the stage where they were disarming each other, Vader would have a considerable advantage, since if he could snatch Voldy's wand out of his hand with the force, Voldy would be pretty much defenceless.
This. This has always struck me as a somewhat silly limitation of wizards in J.K.'s universe (bear in mind: I'm more a DnD/Tolkien-type). IIRC, Rowling has come out and said that wands are not an absolute necessity for magic, but that they are a considerable aid in focusing the energies involved, etc. Still, while Voldy flew unaided, he didn't to my knowledge ever demonstrate the ability to use magic without a wand. (Were I a magically gifted person in that universe, that however would have been one of my long-term goals in the study of magic as it clearly would have presented an uncommon advantage, and it seems odd to me that none of the more senior wizards had at least tried to do this.)
I think we should say the fight happens when both villains are at the peak of their powers--storylines otherwise should not affect the death match.
So this begs the earlier asked question: Horocruxes or not? 
Without the horcruxes littering the battlefield around them for Vader to figure out and destroy, their existence gives Voldemort a near instant win. As it is "to the death" not "to a death", Voldemort can repeatedly die and return to attack Vader again. If Vader doesn't know how, he would probably eventually lose or force a stalemate by imprisoning Voldemort in a manner such that he didn't die and could not gain access to magical materials. If Vader sought out an answer, then it seems we get Vader hunting down the horcruxes. (This all assumes Vader can kill Voldemort repeatedly; see below.) So, I have to say Not. Height of Voldemort's power without having made horcruxes. (Do horcruxes also contain a portion of Voldemort's power (making them even more like Sauron + One Ring)?... (though that's doubtful because we would have expected Voldemort to keep them near him then)
Vader's mastery of the Force is such that he wields telekinesis at will (without the mental struggles displayed by Luke). Voldemort's powers are not at will but require an utterance, etc. It seems then that Vader would easily disarm Voldemort and probably shortly thereafter realize that Voldemort is little more than human when he doesn't have magical means at hand. (This relies somewhat on Vader's comprehension of what Voldemort is doing.)
If Vader doesn't understand what is going on and if Voldemort opens with the killing curse, Voldemort could well win.
Vader: disarm, kill->force telekinesis
Voldemort: killing curse; requires Vader to not recognize the attack for what it is (perhaps he finds it laughable, etc.)->magic, duh
Giving Vader the benefit of the doubt in terms of perceiving the threat to be a threat, Vader's ability to exert physical forces on others to their disarmament, physical harm, and death (probably in that order too in this case) AT WILL and WITHOUT NEED OF EXTERNAL AID nicely hands him the victory.
EDIT/UPDATE: Apparently, according to the HP wiki, wandless magic is a lot more prevalent in the film adaptations while in the books magic is almost exclusively performed with wands (except for under-age magic which is done without great focus or control as a sort of magical self-defense or tantrum). I should further point out that most of my knowledge of the HP-universe is secondhand or from the films.
Still, I already voted and I can't change that now though I'm not sure whether I would or not.
Poll
