An ATP is an ATP. One's no better than the other. I happened to take the 135 portion of the written since I was working 135 at the time. Today, most operations of regional/commuter are 121, so it would probably help there; but an ATP is an ATP is an ATP.
I took the 121 ATP (for obvious reasons). Studied everything BUT the flight planning portions of the test. Heck if I was going to spend an hour calculating time, distance, and fuel to pick one of three answers that are like 50 numbers apart! I got an 84%!