Sniper rifle in games. It's slower, but I've always been one of those guys who feels the point of a fight or war or battle is to do as much damage to your enemy's forces as possible while taking as little as you can. It's why in games like Halo and Gears of War, I hate when the allied AI dies, and why I always try to preserve troops in Total War games rather than going for the phyrric victory. Thus, using a sneaky or stealthy approach is my preferred method, and taking out my enemies from a distance is much better than going all out and charging in guns a'blazing. Besides, it's often better to deal with enemy snipers this way as well, by counter sniping, rather than letting them get a shot in first before you see where they are. Plus, the scope is good for scouting areas without getting too close, so you can come up with a decent strategy.
And in real life, I have to say this pretty much applies as well, at least those points that translate to the real world rather than video games. Again, my favourite weapon is the sniper rifle.