technically the sniper guns will incur the same amount of damage with minor variations. like the r700 & .50 cal have identical damage characteristics, with the exception of if the target is behind something. the .50 cal has better penetrating power, but that is the only damage characteric that is different. but, all the snipes will kill with a single hole in the helmet. (unless they juggy, or you use stop pow to cancel the juggy out)

Or, like the M21 damage char views a 'neck shot' the same as a torso hit, where the other snipes view it as a 'head shot' damage-wise. So I would say it mostly comes down to what you feel most comfortable with. Especially between the drag, r700 and .50 cal...