The A1 is the best. I think.
I have a little story though. I had an epiphany yesterday. I was fondling my guns. I had just recently put an A1 on my Colt A2, because I just like them so much better and I plan to shoot it more coming up here. So.... But then I also have two RRA lowers on other builds. So I noticed that the original colt A2 grip that came on my 20" A2 was fatter and felt better than the RRA run of the mill A2's. Enough so that it makes it almost passable. I might stick that one back on the A2 to keep with the theme. The colt one is marked with a "4" on the inside of it. The RRA ones had no markings.
So.... I didn't really realize how much of a difference there was but I had heard that there was some variance. The Colt one is a lot better than the RRA ones. Which are probably like most of them out there now.
A1's rule though. I haven't tried a crap ton of grips, but any of the ones I've tried pale in comparison.