I'd say Krav Maga. It's a "win at all costs" style, specifically designed for actual real-world fighting instead of just exercise, even incorporating stuff that works from other martial arts. It's meant for finishing the fight as quickly as possible, going for vulnerable areas like the eyes, punching the neck, kick to the groin, anything that'll disable the other guy and leave him vulnerable.
Difficult for me to comment in great detail. I've never studied it personally, and I've never sparred with anyone who had more than a casual exposure to it.
However, as I understand it, one of the underlying concepts behind krav maga is that it's intended to get people "functional" in as short a time as possible. This is why it's taught by militaries: they have a limited training time, and other priorities. Soldiers need to learn to shoot, maintain equipment, drive vehicles, whatever. Hand to hand combat is not a priority, but it's something that does need to be covered...so the goal is to teach as much as possible within an extremely limited time frame.
If you only have a few weeks to train, and that's it...krav maga is probably a good choice. If you're looking for a "full" system to train with specifically for the purpose of becoming a fighter, I don't think that's something krav maga is really intended for.
Anyway, again: it comes down to what your goals are.