@Liam - the Glock construction and way of shooting is pretty similar from model to model. If you’re looking for concealability, you may want a compact or subcompact model. Keep in mind the subcompacts are going to be a little harder to shoot because there’s just less “gun” there to manage the recoil or the grip.
If you are not looking to conceal, take a look at the full size frames as well as the compacts.
I like the .45s My hubby shoots the .40 cals, my granddaughter shoots the 9mm. I think we’d all like to shoot the 10mm. Don’t buy the .45GAP - its not that common a round so it’s not practical. I’m probably going to add a 9mm to my stable soon because it’s cheaper to practice with than the .45 (BTW, even my 100lb granddaughter shoots my husband’s .40 with ease and accuracy, so you really can choose what suits you.)
You probably don’t need the MOS - but… fancy optics
Grip width matters a lot to how the gun fits you, so if you can try both double and single stacks, and the standard vs slim frames, that will help you decide what works for you. I like the fat doublestacks. My granddaughter likes the slim grips. My hubby shoots all of them with a grin.
Generation is another thing to consider. We’ve had Gen 2, Gen 3, Gen 4.
You’ll have a hard time finding anything that’s a Gen 2, so skip that one. My hubby has had several, but there’s not that many on the market anymore.
The Gen3s are solid and capable and probably going to be a bit cheaper, I’ve had my G21 .45ACP Gen3 for over 20 years, and it still shoots just as reliably as when I got it.
The Gen4s have some additional features like interchangeable backstraps for the grip so you can adjust the size. The stock grip fits me just fine, so I don’t need that, but for some folks it’s a boon. Look at the Gen4 options and see if they’re things you care about.
Gen5 differences include differences in the finger grooves on the grip and different grip stippling, ambidextrous options, standard night sights, and some internal changes. IIRC the mags are not interchangeable between the Gen5 and earlier gens, so we’ll probably stay out of the Gen5s.
You can compare the different models here: