ZBrush is a different beast altogether. You cannot paint Specular, Gloss, Emissive, or any kind of special maps. You can only paint the Diffuse, and the diffuse relies on your vertices, meaning it stories the color information on your model instead of UV or textures.
Look up Vertex Painting to see what I mean, ZB does that, but on millions of polies instead.
I personally use ZB since getting your other maps is pretty easy once you have a proper AO, Diffuse, Displacement and Normal Map, especially with xNormal/nDo2 involved, but if you can get your brain wrapped around 3DC, I would suggest that.
Ofcourse, with 30 day trials for 3DC, ZB and Mudbox, you could always try and see which one fits you best.