The Batarian Overlord.
A very underused character. I'm not sure I've ever seen a pug using it. Which is a shame because he is ridiculously effective, and have an answer for anything the enemies throw at him.
Group of shielded enemies? SN -> shoot (not the incapacitated one) -> Shockwave. With the Electric field and Tech burst nobody should have shields left so they are vulnerable to the Shockwave Lifting effect. They won't even have a chance to harm you.
Armored boss units? Slow them down with SN, set off tech burst on shields, and set off fire explosions on armor with Shockwave. With the 8 second DoT duration you shouldn't even worry about enemy shield regen.
Phantoms? Stagger them with Graal so they can't use their "f*ck you" bubble or dodge and then net them. A second shot should take care of them. If not set off fire explosion with Shockwave. Or if you prefer you can also aim SN on the ground and lure the phantom in it, that way they can't bubble or dodge it either.
You don't even need a sidearm for Guardians, you can either mailshot them with the Graal, or if you can't aim like me than charge the Graal then use Shockwave, that should clear the shield out of the way and then shoot.
He's even better at CC than his Soldier brethren. SN slow on armor, SN incapacitate, SN Electic field stun, Tech burst, Shockwave stagger, Shockwave Lift, Graal, Blade Armor melee damage return. With all this CC and the Geth Scanner you should hardly ever take any damage.
In case you manage to get close to death (you scrub) then run around a corner and spam Shockwave for the stagger until you get your shield back.
I have an easier time soloing with him than the Soldier, which is regarded to be a very effective solo character.