I’m around level 35. My playgroup all run shotguns so I typically use the marksman rifle to provide covering fire ( the counter sniper is awful, don’t bother). Light armor every mission; armor rating is bugged but besides that you can out run anything except chargers; just remember to kill hunters and stalkers.

Expendable Anti Tank every mission. Every minute you can kill a charger or another elite. They can also take out bug nests and bot factories. Just throw them out and let your team use them if they want to. Every minute you have a strategem to drop on someone’s head or into a big hole. I can’t stress enough how great it is to have these.

Autocannon/Railgun. Auto Cannon can take out nests, factories and eggs. If anyone else decides to help reload you can go full automatic and kill everything. Remember to reload yourself between 1 and 5 shots to get the quick reload. Railgun is mostly to 1-2 shot hulks in the eye. Otherwise it can kill anything if you are alone.

Then free slots for experimentation. I like the gas for softening groups, all eagle gems are good, and the 380mm barrage for killing my friends. The personal shield is great but I am not a coward.

The mortors make exterminations a cake walk. I otherwise avoid the turrets since they aggro everything around you and I usually walk around every pack. I may start using them as a distraction though.