The ICR-1 Is a lightweight weapon, wich makes it good for training. It has high damage and a moderate fire rate. The ICR-1 can be obtained Via. the Mystery Box.
The KN-44 is a great gun for multiple strategies. It had a fast fire rate and unnoticeable recoil. The KN-44 can be obtained from a Wall-Buy.
The M8A7 is a pretty poor gun. It is a burst fire, wich isn't very good for Zombies. It can only be obtained Via. Wall-buy.
The Shieva is only good on the lower rounds. It is in the starting room of almost every map. It has a low fire rate as well as low damage. It can be obtained Via. Wall-Buy and Mystery Box.
The HVK-30 is a decent weapon. It has a very fast fire rate, that the damage doesn't matter. Combined with a double tap, this is a great weapon, for training and camping.
The Man-O-War is has a medium rate of fire. It has strong damage. This is worth picking up if you're playing The Giant or camping, if you're training you might be better with a HVK-30 or ICR-1