Gimme' my Sig.
It all depends on how you play. That, and which one you spend more time with.
I hated the Sig when I first used it. Now I swear by it.
True, its recoil is greater, but I like the full auto and the sights. I like the fact that with the Sig, I know I can hit something when it's in my front sight. Sometimes with the M16, the bullets just seem to have a mind of their own. Then again, that's probably because I can never line the sights up fast enough for my finger.
In my experience quickly tapping fire will give me some nice, relatively tight two round bursts. Of course that's aiming center of mass, which always seems to make the second round a head shot. Also, CQB is something I think the Sig is really ahead of the M16 in. Like JKJK said, hold the trigger and everyone in front of you dies.
As for light sniping, I think the M16 is better. You can get a second, accurate shot off faster.
But, I can't really snipe with my ping so I stick to CQB.
Crosshairs? We don't need no stinkin' crosshairs!