The Resistance in general would probably use whatever they could scavange. However, larger groups or people who knew military access codes or were hiding out in mitary submarines etc. would have access to better weapons. The weapons I recognised from T4 were miniguns, Desert Eagle, 10mm(probably), M4, some kind of combat shotgun used by Kyle Rease (if anyone knows what type it is, please edit it in). So far John Connor's favourite appears to be a Colt M-4 carbine with an M-26 Modular Shotgun System attached.In 2029 you can see the resistance useing plasma guns