Owning a firearm is like having fire insurance -- if you wait until you actually need it, you won't be able to get it
A well-made, inexpensive used revolver would be a good first choice. Anything by S&W, Ruger, or Taurus in .38 or .357. Simple to operate, ammo can be bought cheap so you can practice often.
Realisticly, I don't expect swarms of Jihadis in our neighborhoods -- that would be brought to a stop right quick. Perhaps more like suicide bombers in malls, or walking into Christmas Eve church services. Most valuable would be the assertiveness to challenge somebody who obviously does not "belong" and see if this makes him suspiciously nervous. By "challange" I don't mean draw on somebody without cause, but if a young middle-eastern-type tries to walk into evening Mass wearing a bulky trenchcoat, a "Hi there! Haven't seen you around before -- did you just move in?" would seem appropriate
All kidding aside, I got pretty freaked a few weeks ago when I drove into my neighbourhood and saw about eight guys in swat-black, stacked up at a front door like they were about to make a "dynamic" entry. Every damn one of the was *swarthy.* I didn't notice weapons, but do you really need them to "practice?"
YOU have hit on the one thing that most people DO NOT have. The plain old steel balls to 'obliquely' question a stranger. Most folks want to sit and wait to see if the stranger does anything.