Hello, Quilter. I have both a Bushmaster/Colt Hybrid 20" and a Rock River Arms 16" Carbine (mid length handguard and small buttstock). Here is what I found:
1. Finish is close to the same to me, but as you said this is insignificant.
2. Both guns have never failed on me. I abused the Bushmaster and I abused the RRA Carbine (which is very compact) in the range and they're both very reliable. Abuse meaning, fire the guns and not clean them until 500-700 rounds later. I do this to test the reliability. As far handiness, I prefer the RRA compactness (mid-length Handguards/smaller A2-lookalike buttstock) even compared to an M-4 or the Colt 653/CAR-15. Of course, the compactness has nothing to do with the makers.
3. Chromed-bores, if you abuse the gun in the field like the Military does, then Bushmaster wins. If not, then both will do fine.
4. I'm not sure about the accuracy question, as they are both similarly accurate. I'd say both are 1 MOA depending on the shooter, I'm not that great of one.
5. Trigger, RRA trigger is smoother and has a better "click" to it. I can't explain it any other way :-)
As most everyone agrees, either gun will do fine.
Cheers.
PS. This is my first post since AR15.com was renovated 1 1/2 years ago. I used to be an active poster back then. Sorry it took so long to come back.