I am a Pro Staffer with Aimpoint, so I get this one alot. My favorite is by far the Comp M4S. They aren't cheap, but they will probably outlast you and your gun. If you are looking for under $400.00, take a very hard look at our C3. It is essentially a M3 without the same level of water proofing and NV capability. I sell these to a lot of patrol cops. THey have the 50,000 hour battery life (you leave our sights on all the time, and they don't turn themselves off), you can get a 2 or 4 moa dot, and they are submersible to 15 feet (which covers falling in a pool or stream, but they aren't designed to be dived like our other M series sights). For the money, they are a flat steal.