I own both the glock and the USP. Both are great weapons. Obviously they lack the power of mid-range aeg's but for close quarters they are fun as hell to use. The full auto feature works wonders with both guns. Each gun will go through a 30 round clip in about 2 seconds. Another thing I love about these guns is that they're so quiet when shooting, much much more than a regular AEG. Dry fire is kinda loud, but shooting actual rounds on full auto sounds so cool. You can get 80 round highcap mags for the glock very easy, but good luck finding one for the USP. Dont get the TM ones, they dont work. You can rig the glock ones easy to fit the USP but cuting a notch where the USP's mag catch is, but you have to do it perfectly or you mill misfeed all over the place. Oh, and they have this metal rail attachment for the glock for adding an optic and/or silencer but dont get it because I had problems with mine and its low quality. I havent gotten my hands on the M9, but b/w those two guns mentioned above they perform about the same so it comes down to style and ergonomics. I'd go for the glock due to the abundance of hicaps on the market.