Signed Sauer for the win. Not cheap, but you can bet your life on one. As for caliber, it’s the biggest one you handle with accuracy. Shot placement counts. Train.
I can not recommend anything higher to an undecided shooter like you than a Sig P320.
They are Glock-simple and dependable (without the wonky grip angle), striker fired, and totally modular.
The modularity means you can buy one pistol, then if you should wish to change size or caliber, all you need is the X-change kit which is like getting another pistol for a couple hundred dollars off. All these pistols use the same trigger module so you can go from 9mm to .40sw to .357sig, sub-compact, to compact, to carry size, to full size with what is legally only one firearm.
Maximum flexibility...and we all know “blessed are the flexible, for they shall not be broken.” ;o)