The RAS is the best choice of those two. The Samco systems are nice for what they cost, but do not compare to the KAC or ARMS systems. The RAS II will free float the barrel and provide a more rigid mount for optics over the long run. The RAS II will remain stable as it doesn't rely on the delta ring to retain it on the weapon. Eventually the delta ring is going to loosen and any system that depends on it will loose its rigidity because of that problem. However, if you don't plan on using forward mounted optics or laser aiumers, then the Samco will be just fine for the job.
I don't have any experience with the Pelican lights, but they seem to have a growing reputation for quality and durability. It is probably a better choice than a G2 for weapons mounting. I believe Pelican makes a weapon light in the same price range as the G2, although the G2 is plenty sturdy. I however, prefer not to take chances by mounting a handheld light like the G2 on a weapon, but many (including the 101st) have done it and with great success. Personally, I wouldn't take the chance unless it were my only choice.
Just be warned that the Pelicans haven't been around that long. They seem to be very well made, but only time will tell. The only sure thing right now is a Surefire Weapon light. The classic series are only about $180 or so. If you are using the rifle for duty or defense, saving $150 on a light isn't worth a life. However, if it is for any non-life threatening purpose, you should be fine with the G2 if you replace the bezel with a shock isolated unit.