A few months ago Garand Thumb was on a Podcast (The Art and War Podcast to be specific) he has been on twice and on one of the episodes he discussed going to a fan event with Matt from Demo Ranch and that every fan there was between 5 and 10.
You most likely want a 9mm, polymer framed, striker fired handgun. Your body characteristics will determine what kind of 9mm, polymer framed, striker fired handgun will be best for you (some people can get away with Concealing a Glock 34 with a light and optic while others have to carry a stock Glock 26 in order to not make it obvious that they are carrying). After finding a 9mm, polymer framed, striker fired handgun you like, you should acquire a carry permit (not necessary if you live in a state with Constitutional Carry, 20 states have it and more are working on passing it) and get a Kydex (NOT Leather) Holster of either the Inside the Waistband or Outside the waistband variety. If you feel it necessary take a shooting course but definitely watch a lot of videos, read a lot of articles and invest in high quality defensive ammunition such as Federal HST or Speer Gold Dot. It is generally recommended that you carry with a weapon light (thus you will need a holster that can accommodate one) Also you should probably shoot a couple boxes of FMJ to get acquainted.
Now if you want a long gun exclusively for defensive purposes the answer is AR-15 with sling, optic and weapon light.