guns

I don't like the recoil of 7.62mm. My shoulder becomes bruised after a dedicated target session with it. It's like 60% as bad as a 12G shotgun. It's also really loud and the ammo costs a lot unless you get cheap steelcore surplus that you can't shoot indoors.

An AR-15 is the smart option if you can only have one gun. It's point-and-click though, so accurate out to 100m that it isn't fun to shoot. The ammo is also pricey enough that you spend a lot of money to practice with it.

The rifle I like shooting the most is a 10/22. It's still lethal in self-defense, but it's cheap and fun to shoot on a range. It's quiet and I can fire 500 super cheap rounds through it without the recoil hurting. With the takedown models and backpacker stock, it's a really versatile survival rifle that fits in a small daypack. When taking someone shooting for the first time, it's the gun I feel comfortable training them on because anything heavier risks them dropping it in a panic. It fits 10 rounds and is mechanically reliable over long shooting sessions.

edit: Also at the ranges I'd expect to fire at in self-defense, within 30m~, I'm more effective with a 9mm handgun than an AR-15. The smaller gun and lower recoil allow me to get more accurate shots off in the same amount of time, especially with any kind of movement. I think it's the most versatile and well-supported rifle, but the size means I would at least choose a 9mm carbine over it if not a handgun if shit hit the fan. Concealment and indoor/close range utility will get you further than the mid-long range shooting it's good at.