Most of the time, humanoids. Jedi, Sith, Gallifreyans, etc... Maybe even a normal human.
I will occasionally roleplay something else, like a cat for example (Since my character is a shapeshifting Timelord, I guess you could say I do rp animals a lot too) but I'll go right back to humanoids within a minute or so, or roleplay them /mainly/.
It's got to be any sort of humanoid, really. Male ones, particularly with a beard. BC