In before someone says Glock.
My suggestion, find a buddy who owns guns and try a few, then go to a rental place, like Granite state range in southern NH, and try everything they have. Find what you like, and go from there. I think you will find tho, the same way you dont have just 1 wrench, you wont have just 1 gun, ill give you my example/ I love history, so for my first gun, I got a 1911. I loved it, its a tack driver, sexy gun, and fun to shoot, but I quickly realized it sucks to carry. From there, I kept trying striker guns, and realized I really liked how the P365 felt, and got it for carry; its small, accurate and holds 10 rounds, perfect for that roll. Then, I realized that if something goes bump in the night, i wanted something with more capacity, and capable of holding a light, so I kept trying a few more, and eventually arrived at a P226. I liked the SA trigger, but liked having the DA for that first pull, I could also attach a light to it, and the heft helped me stay on target. Its great for a nightstand gun, and awesome for the range. Basically, its up to you. I dont love striker guns, so I went with SA, but it may not be the case for you.
I dont think this is what you should do, .as again, you should find what works best for you, but if I had to choose just 1 gun to have, id probably go with a P226 legion. I prefer shooting the 1911, but I find the P226 more versatile. That being said I wouldnt carry it. So i guess I go back to having atleast 2 guns, cause I love me that P365!
Next stop, rifles....you need atleast like 3 or 4.
Edit - Dammit, got beat to the line with the glock comment.