Glock 17.
I have owned almost every caliber under the sun. At this point I like SHOOTING, not tinkering for reliability, and not pretending that zombies are going to come. And don't get me started on the "heirloom" argument....

The G17 holds 20(+2), doesn't have sticks and flags and monkeys that stick out giving you indicators and indications of tactile things you should already known. That gun doesn't need hundreds of rounds fired to make it function properly, like some "high quality" brands. It doesn't require you to take a loan out, to purchase.
9mm is easy to load, it's cheap, it's available.