My first "real" gun was a Ruger 10/22, which shoots 22 long rifle, while my first concealed carry pistol was a Smith & Wesson 9mm Shield.
My grandfather owns a varmint gun chambered in 22 Mag, which we often shot growing up.
To say I have a lot of experience with both calibers as a gun owner is an understatement.
I believe each caliber has its proper place, and both should be in your gun safe.
However, that doesn't mean they should be used for the same reasons. Each round outshines the other in specific instances.
As we compare the .22 vs. 9mm, you'll see why I believe everyone should own both for different scenarios, but if I were forced to choose just one, it'd be the 9mm because of its reloadability and higher knockdown power.
Read .22 vs 9mm: Should It Be a Debate? at Ammo.com.