I love almost every gun/non-gun this game offers, heck, I enjoy the single shot shotgun, but I hate the mercy with a passion. Even made a character dedicated to exploiting mercy--just can't enjoy shooting or even holding the gun. The same thing goes for grenades and plasma casters. I love explosives and plasma guns, but I avoided the previously named weapons.

What weapons do some of yiu dislike even if it is irrational (terrible or amazing)?

Heresy!

Mercy is the one, true weapon.

But me? I hate lever-actions.

One too many hiccups.

Single/double shotguns are just the worst. Most pistols; the exceptions being Mysterious Magnum, Lucky & Maria. Lazer rifles aren't all that good (with the exception of the Tri-beam variant) but at least they've got a decent fire rate.

10mm pistol - it just looks awful. Like a box with a trigger.

Edit - oh and laser weapons. It's that "pew pew" sound which ironically makes me realise that I'm playing a computer game, not exploring a post apocalyptic wasteland with potential death all around. Yes it is petty but it's the reason I've never used Energy Weapons.

At least with guns you get a proper "BANG!" sound. Sounds more realistic and for me, more immersive.

Gauss gun type weapons. I like the design, the lore, the sound, hell everything... but unless you mod it all to hell, has a tendency just to knock people off their asses rather than blowing their heads clean off. That just annoyed the [censored]e out of me. I want a weapon that functions every single time, not a gun that sometimes decided that my enemy needs a second or third chance. Mods exist yeah, but the bugs carried over from FO3 which I thought was kinda sloppy.

9mm SMG and Plasma Caster are too ugly to use.

Oh yes - grenade rifles and the like. They always seem to expend far too much ammo to kill a target. Useful against larger groups to weaken them and take them out with a primary; they're more of a tatical weapon which is not enough of a reason to use them as your primary. They're far too impractical to use in hardcoe mode as the ammo is too heavy and not all that common.