Outside of america - handguns are very rarely carried by other than criminals and law enforcement officers.
Plus handguns are a really bad choice - unless you're intention is to kill.
Even the best shot can't guarentee that they won't nick an artery and have the victim bleed out.
Let's try and concentrate on weapons that:
1) can be carried and obtained easily worldwide (rules out guns)
2) are not usually lethal - obviously any weapon can be potentially lethal. But the object here is self defence not murder
3) possibly weapons you can make yourself.
4) things that can be easily carried and concealed as well as easy to deploy should you need to.
5) where possible the weapon should be legal to carry. In the uk that rules out: knives, extendible batons, tasers, any kind of firearm, air pistols, bb guns and just about anything else a drunken youth can use on another drunken youth.
You can still get away with walking sticks and combat umbrellas (I did not make that last one up).
Avoiding fights is generally the best option, though apparently not for mauro, who does seem to get into a helluva lot more fights than any other 100 people I know.
Even when i was at college and used to go out hunting muggers - I never managed to find one.
Some people are just born lucky