The pistol is tied for having the most zoom in it's alt fire in the game, only matched by the plasma rifle. This makes the pistol incredibly useful for sniping, as it has basically no spread, recoil or screenshake while aiming down the sights. However in the later levels on higher difficulties, it may be better to use the plasma rifle's homing beacon as while it uses lots of energy ammo, more damage is dealt and it auto targets itself for you.

The shotgun is your workhorse for basically the whole game, with it's only fault being it's slow rate of fire. however, the shotgun is the only gun in the game that has an "infinite mag". when you quickswap the shotgun (firing then swapping to another weapon, then swapping back to the shotgun to remove the pump animation), it counts for it's reload as well. While quickswapping the reload only gives three shells, you can just quickswap reload again for an "infinite mag". no other gun in the game can do this, which gives the shotgun an advantage over the super shotgun and later found auto shotgun.
just to note as well, you dont need to left click every time you fire when quickswapping, you can hold down left click and it auto fires for you, much like in doom 2016 and ultrakill.

While the shotgun works best with quickswapping, any gun in the game except the rocket launcher, arc rails alt fire, and full auto weapons can be quickswapped. The grenade launcher already has extremely high damage for it's okay range, all six rounds can be quickswapped for a disgusting DPS. The alt fire can be quickswapped as well, by releasing the right click right as you swap to another weapon. this will detonate all sticky bombs instantly, letting you control them much better.