I'm kind of inclined to lean Voldemort really simply because his combat tactic of "teleport like crazy spamming Avada Kedavra" is pretty effective against anyone that can't block it, but it depends on how fast Rand is able to move and how well he could Balefire a rapidly moving target. Also depends on personality, where Voldemort may or may not be able to tell Rand is enough of a threat to really go nuts on, and how likely Rand is to throw out Balefire right away.
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We clasped our hands, our hands in praise of a conquerors right to tyranny