Old Faithful, modded into a one shot kill sniper rifle and a nearly unmodded Deliverer with just the top damage mod for lots of vats attacks from stealth (lots of one shots enough to kill a cemetary full of ghouls)
for melee its a Extended Ripper. all you have to do is stand there and hold the button, barely even aim and melee enemies will run up and kill themselves on the blade... its lethal in vats due to the massive amount of bleed even without a legendary prefix (i would love one with a good prefix)
at start before i can do these tho, i use a Auto Pipe Rifle i have dubbed "metal Storm" thats maxed out giving it almost no recoil when ADS and can burn a Deathclaw pretty easily (and your ammo) i use it like a mini Minigun for tough enemies while a Long Barreled Double Shotgun i name "Pa's Fishing Aid" after a cut item from fallout 3 is used to one shot most weaker enemies.
i also have a .44 pistol call the "Marston" which has a legendary bleed prefix... its really good in vats with head shots since the bleed will kill anything the crazy base damage does not. i have not used it in ages tho due to the low amount of ammo i have for it.
i dont really use anything else than these items... i dont use the Metal Storm or Pa's Fishing Aid anymore since they are effectively replaced by Old Faithful and the Deliverer and that Ripper.