1) If forced to, fire your weapon to stop the threat. Do not shoot to kill, although death of the perp is a likely outcome of stopping them. Double-tap center mass; assess effect, double tap again if necessary. Immobilize the threat.
I disagree on a legal stand point, if you fire your weapon "your life was in danger and or your families life and or the life of another was in danger"... Deadly Force is Authorized under any states law.
Don't shoot warning shots, don't try to shoot for a knee cap, when you fire, you shoot to kill to defend your life.
When the LEO's show up they're going to want your gun, the only statement you need to make "my life was in danger". Then contact a lawyer before makeing any other statements.
Don't say, "I wish I han't had to do it", or jump up in joy over killing, don't ask to have your picture taken with the fresh kill, keep your mouth shut and find a phone book, call a lawyer before makeing a statement.
To the main subject.
You're better off useing something "common" or mildly modified. For the average Joe. Depends on "who you are".
Now if you're Mr IDPA and you wack some bad guy with a race gun... you can fall back on being Mr IDPA.
If you're a US Marine and you have a M4-Gery set up like your issued weapon, you can fall back on that, even though it looks tactical and crazy intimidateing, you've trained professionally with that weapon, it's second nature to you.
If you owned a shooting range that rented class III firearms and you happened to kill an armed robber with an Uzi, putting 20 rounds of a 32 round mag in the bad guy takeing aim at you and it was the closest loaded firearm to you, you'd probly be fine.
Remember: The Police are going to take your gun and have it till the investigation is over, so between a week, a month, a year. So do you want to shoot an intruder with a Beretta 92FS that is easily replaced or do you want to shoot a bad guy with a tacti/cool M4-Gery that has a replacement value close to $3k.
Do you want to use that Kimber Custom II you bought at a gun show for $700 or your dads Colt Combat Commander that could never be replaced?
It's up to you what you carry, if it's off the shelf and it's not a machine gun, you're probly good... remember you were in fear for your life, what you used didn't really matter when the bottom line is drawn.