My first gun was a glock 23 due to ammo type, servicing, reliability reputation. It's small enough to conceal and light enough to not be a problem if I have to carry around. I didn't want the 9mm as it's weaker and will need to land more shots to take someone down so I went up to a stronger cartridge. I suggest start small that is portable. A resolver is great for SHTF as they likely won't fail and usually a revolver can fire two types of ammo. I looked at a revolver as my first gun but I decided to go against that mainly because it's bulky and heavy so I got the glock. I'm happy with it. Shotguns are heavy and big, so it's not really portable. Really depends what your goal is with this first purchase. Self-defense in the open? Hunting? Home defense? Answering that will tell you what you should get first.