For transposed-battery pistol-type lights, I've used SureFire X300 and Streamlight TLR-1. The SF beats the Streamlight on quality of construction, and ergonomics. Dimensions are about the same, with the SF being a little longer, and the Streamlight being a little fatter. I can strongly recommend the SF X300, but the Streamlight TLR-1 will do if you're on a budget. I've had customer service dealings with both companies, and SF is by far easier to deal with. No experience with Viridian or Insight.