MacCool

You can still get Surefire G2's (65 lumens) for around $55 or the G2 LED version (80 lumens) for around $80 or less. The Surefire G2X in nitrolon puts out 200 lumens and those are $95, but the G2's are arguably a little more durable supposedly due to construction of the tailcap switch circuit board. A reasonably good alternative is the Streamlight Polytac (130 lumens) for around $35. The Polytac actually seems to have better dispersion, and although it's reputed to not be quite as durable as the Surefire G2 or G2X, I know guys that have been running them on ARs for thousands of rounds and I've not personally seen one fail. IIRC, the Polytac and the G2's are the same diameter body and fit the same mounts (1 inch). If they're too small, I have used a layer of a cut-up innertube as a shim, or if that's too thick, a cut-up ranger band.

I have always preferred mounting lights at the 10 o'clock position with tailcap switches so I can activate them with my support-hand thumb. I don't like grip strip switches (too cumbersome and tangly and the cheaper ones are definitely failure-prone) and have always preferred quick detach mounts because I prefer to run my rifles without a light and attach it only if needed (permanent mount interferes with my preferred support-hand grip). An acceptable-quality QD mount is one of the polymer styles from CAA, although my preference has been for the lever-detach models such as the VLTOR.