Boxing is probably the best art.
Bruce Lee said a good striker will always beat a good martial artist.
Kickboxing is a combination of boxing and kicking..!! Boxing is ok but realistically if a boxer comes accross a guy who can use his legs effectively he ll have a very hard time trying to get close.
This is because boxers have a habit of leaning slightly forward on their front leg, in a hunched type defensive position - this gives people who can kick an excellent target since there is limited chance for the boxer to avoid the kick attack. This is simply because all their weight is on the front leg. (Of course there are exceptions - if your very quick).
Just take a look look at some of the k1 fights where boxers enter the ring thers one with Lebanner and this boxer dude with american shorts on.(Sorry guys cant be stuff looking)
Kickboxers have a more upright fighting stance which allows greater manouverability with their legs - give better range with kick attacks allows an effective defense vs kicks.
By the way, who would want a gun? Only pussy's would use a gun or a weapon because they cant fight. A gun would mean you intend to kill who wants to do that? Even if you do shoot them in the leg they might die.. Only paranoid people carry guns because theyre scared of other people with guns or/and that they lack skill, strength, confidence to defend themselves adequately. Unless you live in Iraq who needs a gun?... People who post get a gun are fuckn idiots thats not the point of the discussion.
Take the gun away and what do you have? Nothing but your skills if you cant fight lol practice your diplomacy skills "Ahh You dont want to do this I know Karate! Rrrrrraaa!!!".. 2 step running technique works just as good