I have no experience with Rock Island, but I have owned both Kimber and Sig (currently still have the Sig) 1911's and I have a few other Sigs as well. Both were carry sizes - Sig Tacops Carry (4.25" barrel) and Kimber Eclipse Pro II (4"). I've never owned a full size 1911 and I'm not sure what you're looking for, but I can definitely compare between the two. The Sig has a GREAT trigger. So responsive and snappy, one of the lightest pulls I've experienced. The one complaint I have about the sig is it doesn't feel like everything is there in the hands. Like, somehow it needs to be "fuller". The Kimber was one of the smoothest shooting guns I've ever owned. That's due partly to the full stainless frame, but mostly the bushingless bull barrel instead of a standard bushing barrel. On a standard bushing, the opening of the slide is larger than the outer diameter of the barrel, and there's a bushing that sizes the barrel to the opening. In a bull barrel, the opening of the slide is still larger, but the barrel tapers outward and the outside diameter of the actual barrel is sized to the opening. It creates a lot less flex as bullet exits the barrel. That's definitely an option I want on my next 1911. The prices on the standard Kimber Pro Carry II's are actually not that bad if you get them from the right place. The gunshop my girlfriend works at had them for under $950