160mm rotors/caliper will pretty much be a bolt-on, minimal adjustments. 185 and 203 will require adapters to mount the calipers to the frame.
Depending on your size and riding style, 160's may suit, or if your bigger/more aggressive, 185. 203 is pretty severe, most of the time.
I ride a full-suspension bike, long-travel, with 185's f/r; had 203 on the front, but they were TOO strong for my needs (put me on my face 3x in hard stops, once breaking my collarbone). I'm 6'1", about 240, and ride almost daily.
I recommend Avid BB7.