For me a XDM-Mod2 would be at the top of the list. I am not sure if they can do interchangeable back-straps thought and since these are being used as competition guns that might be a challenge for some (but I want it . Second would be a pistol based carbine. Third would be a Springfield XD-Mod2 - 22 (my Mod2 guns are too short for the 22 conversion) and I don't have a XDM in the the stable per #1.