That's really it, besides the obvious choice: Sniper Rifle. I'm on very hard and I've yet to find anything that I've needed the anti-materiel rifle for. The Sniper gets the job done. And the Gobi Scout Rifle is inferior, IMO. It barely does more damage, and isn't silenced. A full modded sniper even weighs less. The only benefit the Gobi has over the Sniper is it's easier to maintain, but Jury Rigging makes that benefit trivial. Considering the Gobi uses the same ammo as the Sniper Rifle, I see little reason to carry it around other than aesthetics.
Well the AM can 1 shot some stuff the Sniper can't (I'm pretty sure the sniper can't 1 shot deathclaws on very hard?), but since you can fire a 2nd shot so quickly I suppose it doesn't matter.
The Gobi's advantage over the Sniper rifle is the extra 1 bullet for short/medium range. And unfortunately because of the stupid 5x base crit multiplier, the Sniper/Gobi will outperform all your other Guns at short/medium in terms of DPS (assuming you got all the crit related stuff so you're at 100% crit with 50% better crits). The extra bullet is significant because it's often a whole extra guy you can kill before reloading.
