TC suck at one on one. Shockwave don't really put much hurt on heroes (only 150 total at lvl 3, heroes get 25% spell damage reduction), and his attack is slow, resurrection only means killing him takes more time. Things like Death Coil and Storm Bolt are hero killers. Death Coil especially with the low cooldown.
I can imagine what would happen if the the DK had siphon mana instead of unholy aura when going hero vs hero.
Best one on one hero would be DH. Mana burn makes the very thing essential to the heroes useless - their skills. Skills (spells) require mana.
Other than that, I think the Dark Ranger, with Silence and Drain Life may fare quite well.