Creyes one wrote...
Adept and Vanguards worst enemy....The Turret
Solider,Infiltrators, Engineers worst enemy the Phantom
Idk about sentinels anyone a dedicated Sentinel? I would guess Phantom as well.
As a soldier, a boomstick evens the score with a phantom. In fact, the multiplayer enemies are so easy to counter if you follow the golden rule: the seven Ps.
Turrets just require a bit of patience and a phantom mostly become a pain if you are unaware. Phantoms are only a real problem if you panic and/or spray bullets all over the place, and using concussive shot is pointless because they seem to be able to dodge them, regardless of range or positioning. Frags kill them quickly if used effectively, and a well-placed barrage of fire or sniper bullet can silence them before a second has passed. What a real professional does to solve the turret problem is focus fire on any engineers and, should thy have a turret already up, hit the cover, wait until a break in its fire, and then put some high-caliber bullets into it.
Turrets and Phantoms are overpowered, but only if you let them become so. It's like getting rid of a bacterial infection, the best way is to be the worst host physically achieveable. By which in game terms I mean give yourselves a long line of sight and cover all the entrances equally, don't let them get into position and they drop like bricks.