I have been trying to play as a close quarters infiltrator and I've been wondering what the best weapon would be. I have yet to unlock the Tempest, is it useful for this purpose or would I be better off with a shotgun? What mods would work for such a weapon?
Definitely go with the shot gun, I've tried the tempest and it just takes waaaaay too many hits to kill anything, not worth the trouble. Granted I've had a lot of fun with it with the Turian soldier's Marksman ability to put out an absurd number of bullets, but it just doesn't kill fast enough.
As for the shot gun of choice, I really like to geth plasma shotgun. It does a lot of damage, can be charged (you can still use abilities while its charged!) and it has a homing ability so if your crosshairs are on a target, even if its really far away, your shot will track and land on it. As for mods, I go with the increased damage and accuracy mods.
The only drawback is its low ammo count, so plan accordingly.