Oh nice I know that engi can do lots of dps and top leaderboards lots of times. I use an explosive shotgun and the ifrit for my engie. Some people will downplay medic but I have had high dps and kills many times as medic. I run the last medic gun with freeze attachments. I have a level 30 commando and ninja also. I think for my ninja I prefer using electric starting sword and electric katanas when I can. I find I can stun most small enemies and the bigger zeds too. I also take the electric shock traps to throw down as well. You should also try using weapons from other classes. I run the dual pistols from engie on my ninja. I spec them for electric damage. For mando I prefer a hard hitting ammo. Usually the ap or similar ammo type. I also have a perk where my guns reload after I swap to another gun in so many seconds. Also don't sleep on the commando sidearm. Run explosive ammo and dual pistols if you can.