For SD use! 1. XS Sight Big dot/small dot 2. TFO 3. Trijicon 4. Meprolight 5. AmeriGlo They all seems to be pretty close, but which one of them have "the last touch"? And of course quality/durability is also a desired factor. BTW: Does these sights come in "one size" or is it like GLOCK OEM 6.1, 7.1, 7.5 etc.??? And if they come in different sizes, then "HOW TO CHOOSE"? I prefer the front sight is below the target.