I work for a large federal agency that just approved weapon mounted lights. As part of the training, we had to shoot with the authorized models before making our personal choice.

The Surefire X300 had the brightest best quality light output. It is built like a tank. My issue was that the sharp serrations tore up your off hand thumb when using the momentary light feature.

The Blackhawk light requires the use of their holster which eliminated it from my consideration. I carry a Safariland ALS/SLS holster. I do not like the serpa duty holster.

The Insight M3 LED had good light output. The switch was user friendly (and non painful.) The plastic body was lightweight. Initially I was worried about this. Truth be told, all of the abuse my light is likely to take will occur in holster. The hard shell of the Safariland holster gives me confidence that the light will be OK.

I bought the Insight M3 LED for duty use.

In building my AR-15, I purchased an Streamlight TLR-1. I have a mount that attaches to the front sight. The TLR-1 has an optional backplate and pressure switch designed for long gun mounting. I ordered them from www.lapolicegear.com They had a 15% off coupon code going (SPRING15) The TLR-1 is sturdy (metal-construction) and has a user friendly switch.