DSR not mentioned yet? DSR with double tap pack-a-punched is the best weapon in zombies. OSK until round 47 and you can get irons by pack a punching it multiple times.
1. DSR 2. Executioner And the rest in random order M16 (the best wall weapon in the best place to run circles and it's good over most box weapons as well), Galil, LMGs
Haven't given the DSR too much try, being a sniper. If it can truly get iron sights though, I might try it out. The high power + piercing would be very useful.
It's good even without irons, and it's actually accurate for a sniper unlike the barrett that goes all over the place. I've messed around shooting at walls, ADSing with double tap both bullets usually land on the exact same spot or a few centimeters apart from eachother. It's really good. I dunno why it gets a silencer sometimes when you PaP it again though.
http://blackacrebrewing.com/hey.swf DotA 2 random player