So if we're only talking aesthetics...

I've always loved the idea of Orc Warlock. But I hate the aesthetic. In the lore, Guldan is noted as smaller, and skinnier than other orcs. But in WoW, your orc warlock has the same big juicy biceps as a warrior. And they look strange in dresses.

But worst of all, Orcs look very silly on horses/felsteeds.

Undead all the way, it's just fits in so well in my mind.

As the guy above mentioned, orcs don't fit on Felsteed. That's a major factor. I say choose the one with the best casting animation, in your opinion. You'll always be casting stuff no matter what!

DO A warlock with a Imp and steed fire.

feral Imp “(‘::{“[wave]”};’)” >____/