I have a 12-gauge Mossberg 500, but I primarily use it for deer hunting with slugs. I want to get a handgun to add to my collection, primarily for self-defense. I don’t plan on concealed carrying at the moment. Glock G19 Gen 5 seems like the way to go, imo, but I’d love to hear any reasons why there might be a better alternative I should look into.
There are lots of reasons why Glocks are popular handguns. Try it before you buy it to make sure you like it and how it handles.
Good alternatives are Walther PDP Compact and CZ P10c, but there are lots of other 9 mm handguns that are great. It also depends on where you live and what you can get easily and for a good price.
Also explore if you are fine with iron sights or want some nice optics instead.
Where and how do you expect to keep, use, and carry the gun?
Most 9 mm handguns made in the last 40 years are good for self defense. The most important factor is that you actually train handling and shooting your weapon.