In general, I prefer a wide-angle beam. It's much better for illuminating a reef and seeing true colors than a spot beam. There are a number of lights that will cycle between wide, narrow, red options. For casual observation use anything in the 1200-2000 lumen range is fine. Only when you get to video lighting do you need anything higher than that. User changeable batteries are a big plus. 21700 cells are the best standardized option at this time.