Shaun, if you are looking to develop basic fight skills quickly, I recommend learning to box and joining the local wrestling club. Both are cheap, both are readily available, and it is easy to find decent quality instruction in both.
I have been boxing for about 9 months now, have been sparring for about 5 or 6 months, and I would consider my punching both usable and reasonably powerful. Wrestling will teach you how to grapple standing, and after a similar amount of time spent wrestling, you will be able to handle almost any untrained grappling attack that comes your way.
If you are looking for a specific art, then you will have to do more research, and you may not necessarily develop a set of fighting skills quickly--there are more frauds out there in the MA world than in the boxing and wrestling world. However, Boffo is right in that it is platform dependent--what is YOUR potential vice the potential of the style.
"In the world of martial arts, respect is often a given. In the real world, it must be earned."
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