I finally managed to wrap my head around the math for the Critical Hit, so I've decided to sit down and do the math. The equation on the wiki is as follows:
Crit Damage = Paper Damage + Base Damage * Crit Multiplier
Paper Damage is the damage value shown in your Pip-Boy, and includes perks and mods.
Base Damage is the damage of the weapon before perks, but including weapon mods.
Crit Multiplier is 1 by default, but can be increased with perks, mods, etc.
My current character has a Laser Pistol and a .44 Pistol. I also added a Plasma Pistol to my inventory via the Console. I then checked damage numbers for the Boosted Photon Agitator Receiver mods for both the Plasma Pistol and the Laser Pistol, and the damage number for the Advanced Receiver on the .44 Pistol. All weapons had standard mods in every other slot, and nothing in the Muzzle slot. I also have no ranks in the Gunslinger perk. Damage values for the indicated Receiver mods were as follows:
Laser Pistol with Boosted Photon Agitator - 30 Energy
Plasma Pistol with Boosted Photon Agitator - 30 Ballistic, 30 Energy
.44 Pistol with Advanced Receiver - 84
These numbers are the Base Damage numbers. For Paper Damage, we double these numbers to get the Paper Damage.
Laser Pistol Paper Damage - 60
Plasma Pistol Paper Damage - 60/60
.44 Pistol Paper Damage - 168
Now, the equation for each:
Laser Pistol - 60 + 30 * 3 = 150
Plasma Pistol - 60 + 30 * 3 = 150/150
.44 Pistol - 168 + 84 * 1 = 252
Out of curiosity, the damage for the Lucky effect adds another +100% Crit Damage, and is easily obtained with the Righteous Authority. If we factor that in for the Laser Pistol, we get 60 + 30 * 4 = 180
Overall conclusion: the Laser Pistol is the weakest weapon you can choose for dealing crits, despite it's higher Crit Damage multiplier. The damage on the .44 is just too high to overcome, even with Legendary effects. The Plasma Pistol, on the other hand, beats the .44 pistol pretty easily, but only because it 'cheats' by having two damage types; while each on it's own is weaker than the .44, both of them together out-damage it. So the best pistol in the game damage-wise for a Critical Gunslinger is the Plasma Pistol, but the .44 Pistol is still an excellent weapon, as the Plasma Pistol has lower projectile speed that the .44 doesn't have to worry about. The Laser weapon, unfortunately, just doesn't have enough damage to keep up with the other two weapons.