Muay Thai
Actually muay thai kickboxing is not known for speed at all, but actually the shear power that comes from each blow.  If the moves happen to be fast its because a dude who IS fast is useing them.  Muay Thai is called "the science of eight limbs" because the hands, elbows, knees, and legs are used to strike the opponent.  Anyone not smart enough to realize an elbow or knee to the gut is gonna fuck you up is a retard.  Don't believe me?  Next time your beating the shit out of someone 30 pounds lighter than you let the kid elbow you in the face or neck before you hit him.  He might just end the fight right there.  Heres some stuff I copy and pasted from wikipedia, a source that I trust.

Because of the power involved with Muay Thai techniques, fighters do not often block strikes like in other martial arts. Fighters prefer to evade attacks by stepping out of range or moving toward their opponent in order to buffer techniques such as kicks.

Though the high kicks to the head appear spectacular during a competition, insiders of the sport claim that the elbows and the knees are most damaging -- sometimes deadly.

The low kick uses a circular movement of the entire body to kick the opponent's leg with the upper part of the shin. When not correctly defended against, this technique often leads to the end of the fight, as the opponent can not stand anymore after a few low-kicks.

getting hit with a shin kick from a Muay Thai fighter is often likened to being hit by a baseball bat.

Other forms of martial arts when placed against the supieror techniques and training of Muay Thai prove to be obsolete. Such cases are in the many fights held in Thailand and internationally each year. These such forms of the arts are kung fu, san shou, karate and tae kwon do.

(for the record tae kwon do is worthless, liken it to yoga and thats basically what you learn from it)

In the last decade, Muay Thai has enjoyed a boost in popularity in the whole world as it turned out to be very effective in popular no holds barred events, such as Pride Fighting Championship and the UFC (Ultimate Fighting Championship) competitions. It is widely recognized that a combination of a grappling art, such as Judo or Brazilian Jiu Jitsu, with Muay Thai is very effective in such fights.

Yeah that shit sounds pretty dangerous to me.  I'd appreciate never haveing to read another bullshit poste from assholes like you.  If you don't know what the fuck your talking about then shut up.

Muay Thai Kickboxing is better than the rest of the shit out there.  Some people think that if you wiegh more your chances of winning are increased...no shit!  This is a comparison of martail arts not wieghts you dumb fucks.  I have no doubt a 40 pound girl would get her ass kicked by a 70 pound class bully regardless of what she knows. on the other hand a 170 pound muay thai kickboxer against 200 pounds of any other fighting style, assuming they are both masters of there art I'd put money on the muay thai.  Well unless were talking mishima style fighting karate complete with lightning bolts and stuff, but thats a whole different story.  If your looking for a nonlethal alternative to a handgun just buy a mace can.  With that I bet you could woop any proffesional boxer, fighter, hell even sumo.
Muay Thai Kickboxing is better than the rest of the shit out there.