Boxing to me.

Does sumo count?!
 

If it does, I have to say Sumo wrestling. If you can get up close to watch it, the hits those guys put in are massive!

I saw them in training, check out it out here

I believe in Bruce 100%, but that philosophy only applies we you have a grasp on how to fight. Bruce Lee soon after said, "Jeet Kune Do is to be an extension of what you already know," meaning that he doesn't shun different styles, but feels that you shouldn't put so much emphasis on style. A TKD fighter can beat a Muay Tai fighter and vice versa: it all depends on the fighter.

I myself am a fan of all Martial Arts, being the American Karate Association's national champion in fighting and team fighting (fighting bare fisted against a group of people to test stamina, endurance, and decision making ability).

I do like Bujinkan Ninjutsu, though, as it works with all weapon styles and 水とん。

Tons
 

there are tons of great martial arts, but it is most important to train.

that is why i like Jeet Kune Do the best. It is fundamentally about improving.

There is no best Martial Art, but now that I think of it, there may be one perfect fighting system, that being Ninpou Taijutsu (忍法体術)

The art is from Bujinkan Ninjutsu, and teaches you to move the way your body naturally moves, instead of trying to make it do all of these ridged, self-damaging techniques.

Jeet Kune Do?

No. Their style sux. Their lineage is fake (not real Ninja). Their training is unrealistic and not practical to the real world or even sport.

I like Muay Thai most. It's easy to learn and train and very effective. Of course, you have to work hard if you want to be good at it (lots of conditioning), but the basic training provides sure results in time.

Here's a vid from my gym of Muay Thai training I made: