I like the sound of the Rat Slayer for a lower damage version of a sniper rifle and the fact that that ammo is plentiful and it's easy to repair - 2 negatives of the GSR but I haven't got it yet.
It's great taking out 5-6 gang members from afar and watching them run around in cricles trying to work our where the shots are coming from - nice.
Finally for close up inside work I use lucky! For my character that's a 70% chance of criticals in VAT and like someone said not much can take a bunch of headshots. I now know where THe Chopper is and I've missed it on 2 occasions -shame on me - I need a 'highlight every item' button!