Most looking forward to Barbarian and Druid for me. I think Barbarian mechanics will fit almost perfectly with the game version of 5e rules, and be really fun and intuitive (and probably a really strong melee class, comparatively, as the fighter and ranger don't feel like super reliable DPS yet). As for the Druid, I think if they introduce at least two subclasses that are quite different--say, the Circle of the Moon as your typical Wildshape-based Druid, and then something weirder like Circle of Dreams or Wildfire--you could have a really interesting spellcaster option that feels totally different from Wizard or Sorcerer (if or when they add sorcerer).
