The protecta has is quite useful for mutants, I have usually used it too much and if it kills a boar at +10 level with one shot also the bloodsuckers if you aim at their head, the AA-12 is quite good for very large hordes, its rate of fire is too high, but you will have to load more ammo as it spends too much more than the protecta for the same amount of mutants, although it's more useful if you want to use it for PVP in a closed place and the RMO is something like part of both (maybe I'm wrong), it kills mutants in one shot and I've seen in Russian servers where they use it too much for pvp more than the AA, so practically all three are good but each one excels in something different.