For my money, the AR9 can't be beat. All the things we love about the AR (mag capacity, after market support, familiarity, etc.) in a 9mm. You can find the PSA kit (no lower) for about $400 a couple times a year. They also just released the Glock mag lowers and their hybrid uppers are supposed to feed both the Glock and Colt SMG style mags. The newer versions are a bit more but I think you can put one together for $650 or so. I would like to see some in other calipers but the 9 is a hoot.