I always use the weakest/most common/starting weapons as much as possible. Usually with the intention of saving ammo for my better weapons for later, or pouring upgrades into something I will always have on me.
Often I don't shoot until I can get a headshot.
I imagine it would freak out my in-game comrades: "We're trying to move forward, sir. It's just that one of the new guys--he keeps popping out from behind cover to try and ping the enemy with an AK-47. We've been stuck in this street for the last ten minutes while he's been dealing with this sniper..."
