OK, without this falling into a guns debate, let me give you just some dry facts.
temper what you read here with the fact that I am an NRA life member (also a member of the ACLU and a host of other traditionally "left" and "right" organizations)

First of all, a gun won't make you safer, won't protect you from harm, and won't do a damn thing to improve your lot in life unless you know how it works, know how to shoot and always remember that shooting skills are terribly perishable.

Secondly, having a gun does not mean a bad guy will magically drop when shot like in the movies. In fact, there's plenty of times that people are shot multiple times and keep coming. So don't think "boom" = "safe" - it's much more than that.

So, without having gone through the whole list of replies to your post, I'll just put in that the guns that are easiest to operate "effectively" - as in you'll probobly HIT what you point at are, in order, a shotgun, a rifle, a handgun.

I can't stress enough how much practice it takes to be a good shot with a handgun. Not just your initial practice, the ongoing, never-ending drilling you need. I also can't stress enough that a handgun requires extra-special dilligence in terms of responsible handling and storage.

If your intention is to scare off a looter, then probobly a shotgun is your best bet. In terms of popularity and usability, it comes down to two choices, the Remington 870 series and the Mossberg 500 series. I like the Mossberg 500 better than the 870, but that's a matter of how they handle and feel differently. In both cases I load my home defensive weapons with 1 round of #6 Shot (a fine, almost kosher-salt sized pellet of lead), 1 Round of #4 Shot (a bigger bit of lead), then 2 rounds of Buckshot - heavy large pellets.

HTH