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
Better get one now, while you still can. If gun sales are suspended on a nationwide level, it will be a Homeland Security "emergency" that does it.