Rifle vs Pistol

Rifle - Pros

• Increased ammo capacity, 66% more rounds per clip. Less frequent reloading and consumes fewer inventory slots, less Encumbrance and space on the Transport. In practice you can get through a mission with between 0 to 0.25 reloads per soldier. With Pistols you need at least 0.5 reloads per soldier, probably 1.0.

• Option of much higher "shock" firepower at very close range (only), using Auto mode.

• Weight not much more than a loaded Pistol, especially if equal amounts of ammo are carried.

Cons

• Surprisingly expensive.
• Two handed weapon, impairs use of grenades and accessories.

Pistol - Pros

• Firepower (effective damage dealt per turn) is broadly the same as the Rifle vs lightly armoured units (Sectoids and Floaters). (Except when the Rifle can be used on Auto at point blank range.)

• One handed weapon gives flexibility with use of grenades, accessories, and scratch-use of second weapons (eg launchers).

• Lower TU requirement gives greater opportunity for mobility, scouting while still preserving some deliberate fire and reaction fire capability.

• Excellent for skill gain / training due to the high number of shots fired per turn.

Cons

• Noticeably less effective vs medium-armoured targets (e.g. Mutons, Sectoid/Floater leaders) and above.
• Ammo capacity. See note above under Rifle.