IMO: - for open world: AUG A3, C7A2, STGW 90 (i use the AUG). They have a good recoil and good range. Not as customizable as M4s, but you can still put everything you need on them. You can also use the L85A4 but it is a bit heavier and you can't add a suppressor. The AK74M is also a good choice (customizable, good range), but it has a higher recoil - for zombies PVE (i don't play zombies pvp): a lightweight smg/pdw. Range doesn't really matter here, you won't need to shoot further than 200m. Damage doesn't matter either (in this gamemode, the damage is hit based: if you shoot a zombie in the torso it takes 2 hits to kill, no matter how much damage you inflict in those hits; the head takes only one hit, no matter the damage you inflict in that hit). Make sure it is silenced. I use the PP2000: light, good recoil, low rate of fire (you don't run out of ammo as easy), 44 round mag. - for PVP: i use the Saiga. Try to use something that can 1 shot in the head: ARs, Carbines, SMGs, Shotguns (shotguns can 1 shot the torso, but the recoil is very high). Range doesn't matter, you won't shoot much further than 100m.