I prefer a clean gun. Only way mine will see a light is if made legal for varmints. Then it will get a kill light mounted during hunting season. Never saw the point of turning a good defense firearm into a 15 pound log.
I prefer the surefire G2L in a gear sector offset mount for mine.
I've tried streamlights and a few other medium quality rail mounted lights on my ARs, and i just prefer the ergonomics of the offset mounted surefire.
I've tried the laser from a streamlight tlr2 on one, and just didn't like it or find much of a practical use for it. I find target acquisition through an eotech is much easier than using the laser.
The only use I have for a laser is for very limited self defense purposes on a handgun. I find them more gimmicky than anything. If I were in combat and had a need to paint or identify targets, then I might find some use for it, and would go for one of the Laser Devices dbals.