45 tends to be a favorite among long term shooters, particularly us older guys. Good stopping power, not so much recoil it's a big problem, and usually easy to get. But it isn't really a good beginner's choice, imo. If you start with it, and get good with it, it tends to set you up very well since it does have enough recoil you have to learn how to stay on target between rounds. However, the learning curve is worse because of that.

There's ammo that's way more potent, for sure, but it's the absolute most kick I'd ever put in a beginner's hands.

Mind you, there isn't really a default ammo choice across the board. It is a very popular pick for personal and home defense. But it isn't ideal for concealed carry for everyone's preferences because you just can't carry as many rounds in a compact form factor. I personally carry a full sized handgun as my concealed carry because I'm a big dude and it won't show, so I carry 45. If I can't handle something with the 14 rounds +1 in the two magazines I keep on me, I'm screwed anyway, so I'd rather have the extra punch.

If I couldn't carry a full sized concealed option, I'd probably either step down to a 9mm, or switch to a revolver in 38 or 357, whichever I could get a good deal on. The kind of ammo in between 9mil and 45 for semi auto is good, but not significantly different performance wise, and tend to cost more since they aren't as popular. Which is why I'd go with 38/357 for a wheel gun. I like cheap and easy to find ammo lol.

Also, as a side note, I've mostly been talking in reference to a general purpose carry and range shooting handgun. Which is what most people asking what you're asking are wanting to know, but there are other applications that might change things, like a desire to shoot competitively at some point, or wanting to hunt with a handgun (which is very niche tbh).

My advice overall? For a first handgun, in the 3-700 buck range, pick up a 9mm, probably a sig or glock since they're popular enough to run into good prices sometimes. Learn how to shoot, get used to all the safety and carry rules, and then figure out exactly what your needs are as you go. Resale value on the popular brands is solid, so you won't lose much by selling and switching to a different caliber in a year or two, if that's where you end up. Same way if you just want a fancier handgun in 9mm, you'll have part of the new cost covered by the resale.