AR-15. With how common they are you can easily find a configuration to your liking and can just as easily find parts and ammo. They are very reliable, easy to upkeep, easy to clear jams, easy to mod, easy to shoot, etc.
I’d also suggest a reliable pistol that holds 10 or more rounds, a Glock 17 or 19 would be my recommendation. They are super reliable, stupid easy to assemble, and take the most common ammo. Just like the AR-15, Glocks are easy and reliable and there is a huge market for things like holsters and magazines.
It’s a Minnesota bill and the link takes you to the full text.