Really depends on your play style. If you are like me and using the rifle as an actual sniper and being sneaky, using Kick, Blind Eye Pro, Assassin Pro and Marksman Pro (also use portable radar and BB's or Clays) lining up your shot, holding your breath and making a couple kills from one location and then moving to another location... the AS50 works great (I call it the ASS-O ). The AS50 does seem to have less recoil due to the barrel design (which does seem realistic IMO) so if you are looking to do the 2 Attachments, it is more forgiving than the Barrett with 2 Attachments in this aspect.
However, if you are just a Hard Scoping (also called Quick Scoping) asshat that's just running and gunning, the L118A and/or MSR are good (mainly because the Mobility with these rifles coupled with the damage and accuracy make it easier to run and gun).
If you just want to pump rounds into people as you move around the map (not really what I consider running and gunning) without worrying about an empty clip every few shots, the RSASS is a nice rifle too.
IMO, the Dragunov is very inaccurate, higher than expected recoil (even with Kick) unforgiving and a disappointment in just about every aspect.
So again, really depends all on your play style. I personally love the Barrett and primarily play using it, but do trade off to the AS50 depending on the map (my Barrett has the Heart Beat Sensor and my AS50 has the Variable Scope).
I don't know man... I've noticed some major recoil with that gun if you're not using Kick and need to make a second shot. I think the bolt loading without SoH is a little over 2 seconds, so you better get a OHK or you're gonna get shot full of holes.
And yes, I totally agree with you on Hard Scoper's... GTFO of my lobby. LOL!
Most people probably wouldn't consider this sniping... but:
I'm a big fan of putting an ACOG on a sniper rifle. The BEST setup for me was an ACOG on a WA-2000 in Modern Warfare 2.
In MW3, my usual sniping kit got ruined. The Dragonov is the natural replacement for the WA-2000, but the high recoil (even with Kick) makes pretty much fail. The next natural replacement is the RSASS, but the low mobility and fairly low damage makes the MK14 a better choice overall.
So having no natural replacement for the WA-2000, coupled with the fact that the maps in MW3 are significantly less sniper-friendly that previous Modern Warfare games, have left me using the bolt action snipers. Essentially what it comes down to is you have to kill them in one hit no matter what, otherwise they will most likely kill you. And the damage/recoil ratio just isn't there on the semi-auto snipers anymore, so I'm forced to use bolt snipers. Either one of them works, they seem so similar to me that I would be surprised if they weren't exactly the same in the game code.
ps. Making it so ACOGs can be affected by EMPs has got to be one of the strangest (and dumb) design decisions I've ever seen.