Honestly my best advice is to go to a gun shop and rent the gun you think you want and several others. Some guns just point better FOR ME or fit my hands better (or worse). Years ago, my Glock 22 was stolen out of my truck. It was in my truck because it was too big to carry unless I was wearing a winter coat. So I decided that I would buy something smaller and easier to conceal so I would actually carry it instead of just in the truck. I figured I would wind up buying the single stack Glock because Glock. I went to the range and told them that I was looking for a compact 9mm, striker fired, and I wanted to try the single stack Glock (can’t remember the model, maybe 43) and the Springfield XDS at the recommendation of a friend who carried the XD Mod2 as a duty gun. I asked the guy behind the counter what else I should shoot along those lines. He immediately said the M&P Shield was one of their most rented guns. That wasn’t even on my radar but I tried it. I shot all 3 and some in multiple calibers (9mm, .40 and .45). To my surprise, I shot the Shield in 9mm noticeably better than the other and I shot the single stack Glock the worst. I tried it again on a different day and in a different order and the Shield came out on top again. There isn’t a thing in the world wrong with those 2 other guns but for some reason I shoot the Shield the best. Your mileage will almost certainly vary. I have since bought a Shield Plus to replace the old Shield 1.0 due to the lousy capacity of the original Shield. I still shoot the old Shield very well. I had an Apex trigger installed along with fiber optic/tritium sights with a green front sight. I have a type of color blindness and can’t acquire a red front sight nearly as fast as the green.
You need to decide what you think your purpose would be for the gun. For instance, if this is to be a nightstand gun then probably something full size will be the best choice. If you think you would like to carry it at times then a compact or subcompact like those I discussed above might be the way to go. The guns that are more easily and comfortably carried will tend to have more snappy recoil than a full size model. Everything is a trade off.
EDIT: The last few that I’ve bought have all been optics ready and I’ll pay more for that if I have to. Red dot sights or RMR type sights are only becoming more and more popular so you may eventually regret it if yours doesn’t have an optics plate. I have a green RMR on my Glock 19MOS and I’m still getting used to it but the difference in speed on follow up shots is pretty extreme. I haven’t put a RMR on the Shield Plus yet for several reasons but I definitely wanted the option.
2nd EDIT: Load up on the magazines that you want once you make your choice. We’ll lose the right to the mags we want before we lose the right to buy the guns.