I have a 20ga. 870 That has seen a decent amount of time on the trap range. I would always keep up with my two buddies and their 12ga.'s. I think alot of it has to do with the fact that I am very comfortable with it. It fits right it swings well and it does the job for me. I traded with a buddy for one round and he didn't like the recoil as it is light. He's a pretty big guy too.
It will boil down what works for you just like with any gun. Me personally I like my 20 ga.
You can't put a gun rack in a Prius!