.357 magnum
The Mossberg 500 series is the best self defense hand gun in the 200 to 300 dollar range.
Impossible to answer. "Best" is a meaningless term until you quantify it. Are you talking about a long gun or a hand gun? New or used? What will it be used for?
a derager , revolver, or automatic
At a shooting range is usually the best choice.
There is any best. Its where you point it. Preferably at yourself.
There is no best gun because it depends on too many factors. The best gun for you is whichever gun that fits your hand the best so you can shoot it accurately. Beyond that, a gun for everyday carry must be reliable and be of an adequate caliber for self defense.
Berretta storm
the G18 The G18 is a machine pistol, not a machine gun. Which category do you mean : LMGs, SMGs
a hand gun
The question can't be answered without knowing what type of shooting and what "gun" you mean (hand gun, long gun, centerfire, rimfire, muzzle loader, etc..)
The best gun for any application is the one that you fits your hand properly and that you can shoot accurately.