It's all about preferance. What works for them, what they're comfortable with, etc. But having a gun that can use full auto and USING the full auto and calling your self a "sniper" is a bit of an oxymoron.
well a paintball sniper is a bit of an oxymoron too... so screw 'tradition' and get a QUIET auto if you like.. i use a tiberius, my team mate uses a DM7 on full auto... if i line up 4 players: i have to pull the trigger and take aim a MINIMUM of 4 times , he just has to keep his aim as he shoots a solid rope of balls. the only difference, is that if someone see's his rope of balls and survive the volley, they know exactly where he is. and it usually takes someone a few shots to figure out where abouts i am. and by then they're usually out, or i'm in deep poo(way to outnumbered), and should retreat ASAP anyhow.
pros and cons of auto
a quiet auto:
can eliminate more people faster and easier
accuracy of shot is less important
do not have to retreat from a fight as often(more firepower)
you're a bigger help to your team if required to drop out of sniper roll
can give a more easily seen visual of your position(stream of balls)
may go through more balls per elimination( and may cause bonus balling)
price! (you're looking at triple the price minimum, think 1k+ for a proper QUIET auto marker, + more air, + more balls, + accessories)
may go through more air
most viable markers do not have rails to mount accesories
usually have a taller profile and center feed tube. (more practice required)
and you can always switch your "full auto" to "3 shot burst" or "single shot" .. so if you've got the cash, go for it.