It's difficult to give you an answer not knowing what the rest of your wardrobe looks like. As for black vs brown, that will depend on what will work better with what you already have.
What kind of leather you want is tricky. I have both a calf DR and a lamb CWU, and can't really say I prefer one over the other.
Calf is heavier, will generally last longer(it's basically armor), but lamb is a bit easier to wear. Calf leather can take a beating, with lamb leather you have to be a little more careful. My own preference would be lamb for bomber styles(MA-1) and calf for a moto(2/4zip) Obviously there are other options, being goat and horsehide, but I'm not a big fan of the grain of goat leather, and horse hide is generally not ideal for everyday wear. It's insanely heavy/tough to break in compared to other options.
With all of that said, you can't really go wrong with any combination