I did some testing with a Five-crank Laser Musket a while back to see how it's damage scaled with multiple cranks. A single crank did about 8 damage to a Deathclaw's back, but more cranks resulted in more Damage than I thought it would. At 5 cranks, it did 68 damage, which is 8.5x the damage inflicted by a single crank. I'm actually going to be looking at using this for my Laser Commander character whenever I get around to playing her, just because I can see that damage getting really, really high with something like "Double Damage to enemies at full health".

It was a bit difficult for me. I had a +plasma damage fully modded .308 but I don't like weapons turning foes into goo. The .50 I consider as too weak. I really don't like shooting the Gauss rifle with this charging mechanic. Trying a Plasma rifle I found it not very accurate and the plasma crawls to the target with the speed of a snail; ok, I could possibly live with that, but I hate green spots all over the game.

In the end I used a combat rifle with a short distance scope and a six-crank laser musket with scope for bigger foes. I despise suppressors anyway, too easy. I don't like the laser musket so much, although it's really strong, because of the noise it makes when loaded and the stupid ability to melt foes to red dots. Now in my second play I found a two-shot legendary laser musket which results in insane damage. Many legendaries are over the top and not a help for a satisfying game feeling but it's up to you to use it or not. I sold most legendaries.

In my current playthrough I have a rule only to carry one rifle (a .308 hunting rifle till now). I will change to a combat rifle with short-distance scope as soon as I find one with full barrel and stock (I only use Gun Nut 1, so modding is a problem). Defending against charging strong enemies with the bolt action rifle is difficult.

So, as a result, there is no best sniper rifle for me. As I prefer powder weapons it would be for me a .50 hunting rifle if the .50 would have a decent damage boost over the .308 rifle.

Agree so much with this.

I think the .308 combat rifle is a superior sniping weapon.
The rate of fire alone allows you to get out of tricky situations.

I've found the gauss rifle to be all but useless in fights that go beyond a single shot. It may be useful if you are hunting Deathclaw but against large groups I would rather have my .308 Combat Rifle.

I was lucky enough to get the +50 radiation damage legendary combat rifle very early on, and while conferring no extra bonus against ghouls, robots and wasteland creatures it cuts down Raiders and Gunners at an alarming rate.

I would love to get my hands on the frame that does double damage if the target is uninjured. I have it on a combat shotgun... devastating against ghouls

The essential mods for my sniper are semi-automatic rifle with scope and suppressor (even the combat shotgun ), which all stack together with the relevant perks for x5.3 damage on sneak attacks (and from what I recall that's all attacks made in hidden and caution stance).

Currently:

Gauss rifle. Have been using that as a sniper ever since I picked one up.

Though I do carry a .50 for backup.(legendary 2-shot iirc)
.308 is ok for followers and settlers.

Next playthrough I don't think I'll use a sniper rifle at all.

I have that on a laser rifle I converted to a sniper, much fun was had.

I picked up Old Faithfull (laser gun with 2x damage if target is full health) last night on a whim. Upgraded it for sniping. I've been really happy with it.

It takes up a bit more screen space but it fires more accurately when not zoomed in. Far better for indoor fights than my Overseer's Guardian.

Looks like sniper play is popular!

My first one was a pipe, upgraded to an Advanced .308 receiver. Then it got upgraded to .50 (with all the other features at max and a suppressor).

Then I found an "infinite" ammo .50 cal. I figured this meant it only needed 1 round and could fire infinitely, but it actually means you never have to reload it (though you need ammo for it). I think I'm going to retire it to full-auto status in a while.

I found a gauss rifle and the damage on it with Rifleman 4 is insane: 330 or something along those lines. I forget if it has any legendary perks on it. I think it does, though it is not particularly good for a sniper.

Anyway, with that much base damage and such a limited magazine capacity, I'm now leaning toward that Gauss becoming my sniper rifle.

My CQB rifle is the "Righteous" thing you get from one of the early quests, with reflex sight. My third ranged weapon is an Incendiary Shotgun, and melee is a legendary Revolutionary Era sword that costs 25% AP and has a stunpack installed.

Nothing else I've found seems ideal for a sniper, and I tihnk "Instigating" is the Legendary trait that would be most appropriate for a sniper rifle. An Institgating Gauss rifle with full Rifleman perks and fully modded could probably take out nearly anything in the game in one shot.