Any shotgun with hi rate of fire, shockwave is best but rare,on level 30 thru 60 I always had an electronic gun, Sunfire, or sunburst, something like that, was a go to gun cause it had decent dmg + rate of fire. In fact it doesn't really matter except whatever your preference might be, for me I put dmg, rate of fire, reload paid a bigger price in my opinion, if I didn't have a weapon that would relatively boost in those characteristics, I. Wouldn't keep it. I modded all my weapons to their highest abilities and got rid of what didn't work. It depends on your class too, ripping and running gung ho, can get boring, I finesse the game when I play solo, certain maps for xp others... well, really for whatever ineeded, now playing with other people, it was easier to let someone do the ripping and running, I would clean up. Each map is only...what 1:30 to play 3:00 minutes? If you play with others different guns for different maps......solo.....have the top of weaponry. I had a set of values. Fire rate below 8, probably didn't last too long, I couldn't upgrade , that probably didn't last to long either , whatever suits you. By the way, it doesn't get any easier, zombos skills grow just as yours do, that's why I am a medic, gas bomb does 50% reduction, that's huge when your fighting by yourself.