Shotguns
The most role-specific firearm on the site. A clay gun, a waterfowl gun and a home-defence gun share a gauge and almost nothing else.
Action type is the first decision and it is close to the only one that cannot be changed later. Pumps run any load that fits and are indifferent to whether a light shell generates enough gas to cycle. Semi-autos shoot softer and faster but need loads above their cycling threshold. Break-action guns give you two chokes, two loads, and a reliability profile with almost nothing to go wrong.
Fit matters more on a shotgun than on any other firearm, because you point it rather than aim it. If a gun does not come up with the bead naturally aligned, that is a fitting problem no amount of practice fully resolves.
Pump action
Mechanically simple, tolerant of any load that fits, and indifferent to whether a light target shell generates enough gas to cycle. That last point is the real argument for a pump.
Semi-auto — field and hunting
Gas or inertia operated. Gas guns soften recoil noticeably and need more cleaning; inertia guns run cleaner and lighter but transmit more recoil.
Semi-auto — tactical and value
Shorter barrels, higher capacity, and lower price points. Reliability with light target loads is the thing to research in this tier.
Over-and-under
The clay-target and upland standard. Two barrels, two chokes, a single sighting plane, and the ability to select a load per barrel.
Side-by-side
Traditional upland configuration. Wider sighting picture than an over-and-under, generally lighter, and increasingly a deliberate stylistic choice rather than a practical one.