I've dabble with a few different guns recently, mostly just ones I picked up off the ground. What I've discovered is that a full-auto AR is more consistent than a sniper.
Say you have a flawless connection. At best you might get a OHK 70-80% of the time. From my experience if you don't get a OHK the target will have run away before you could get the next shot off at least half of the time.
If you have good control and good eyes I've found that a decent long range AR can kill much more consistently than any sniper, MR, or the MSBS. The reason is that the time to kill really isn't that long. It's usually no more than 4 rounds on a bad day. It's also more versatile so it works in pretty much any circumstance and has a larger mag capacity and fast handling to assist with multiple targets.
Fact is, the only advantage a sniper has is a better scope and OHK potential. But good eye looking through a Thermal or ACOG isn't much worse off and the TTK for some ARs might as well be considered OHK.