Which choke & shot?
The right choke and shot size come down to two things: what you're after and how far it'll be. Pick both and this gives you a sound starting point - an open choke and small shot up close, more constriction and bigger pellets as the range stretches out. Then pattern your own gun to be sure.
Small, fast birds - a wide pattern of small shot beats a tight one.
Rule of thumb: the further the shot, the more constriction (tighter choke) and the bigger the pellet. Up close, open the choke so the pattern has room to spread - a tight choke on a close bird is a miss or a mess.
⚠️ A starting point, not gospel. Every barrel patterns differently, and modern loads vary a lot - the only way to know your effective range is to pattern your gun with the exact load you'll hunt, on paper, at the distances you expect. Always use non-toxic shot where the law requires it (all waterfowl, and many other hunts), and never exceed your gun's proof for steel or TSS.