Geth Infiltrator, all the way. I was playing Silver rounds non-stop last night with him, while mainly using the Kishock Harpoon Gun. My friends and I were kicking some major ass.
First off, Hunter Mode is something I can't live without in Mass Effect 3 now. See enemies no matter what in a 20 meter radius, have a higher rate of fire, higher damage for weapons, powers, and melee? Excellent. The only downside is the loss of 50% of your shields, which really is the Geths only saving grace in the health department. I kept getting down to one bar of health, or even downed if I wasn't paying attention.
Second, the Harpoon Gun is a weapon that's been growing on me. I have it level IV now, and its just as powerful as my Widow IX, which makes me think that, stat-wise, its the best multiplayer Sniper, especially in terms of power. But, its handling 'quirks' make it hard to use unless you know how to use it properly. For a slow target, or one that's standing still, its easy. One of the quicker moving ones? Forget it.
But, it has one thing the Widow doesn't have: The Fun Factor. Seeing an enemy be launched back or to the side after being impaled by a Harpoon, is fucking epic. More than once have I done Grunts evil little laugh after managing to one-shot a Phantom by getting them in the head on Silver, and seeing their body ragdoll a few feet away. Like I said, Fun Factor.