https://www.nrafamily.org/articles/2...-fit-a-shotgun
This link will give you a little more in depth answer.
For most people you don't really need to overthink it. If you pick up 5 different shotguns, shoulder them several times each, you will likely feel a few that feel really natural and a few that you feel like you're searching for the bead. It should shoulder naturally and the sights should come into your line of sight. If you are having to search for the sights ( raise, lower, tilt your head) to find them then something isn't fitting correctly.
Keep in mind that if you try the guns out in a shop while wearing flip flops and a t-shirt it might (it WILL) feel a little different when you are dressed for 5deg weather.
Manufactures make a general fit that fits most of the population. But there are still slight variances between them that you may prefer by handling lots of guns. VS just taking recommendations online.
I PERSONALLY prefer a pump. For it's reliability and simplicity and just because that's what I grew up shooting and have thousands of rounds through. But there are lots of auto loaders out there with pretty good track records as well.
-Jake