if you could master any martial art...

Fantasy => Rock Lee's taijutsu.

Real Life => Dual Blade Sword Handling. Two of the martial arts I'm aware of that involves dual blade is Kendo and Arnis.

Oh man, for me it's a 3 way tie between Taekwondo (both the WTF and ITF stuff), Kyokushin Karate, and Kendo

Taekwondo or Muay Thai Kickboxing.

Krav maga, wing chun, and maybe kendo

I've seen a Martial Art once on TV where in a man can make an opponent faint simply by touching sensitive points of the body.
I believe it's called "Death Touch"
That's what I wanted to Master to keep fights short as possible (If its authentic)

(Bare handed)
Fun...
-Boxing/Kick Boxing
Defense (and fun)...
-Muay Thai
Offense...
-Brazilian Jiu Jitsu

(Weapon)
Fun...
-Fencing
Defense (and fun)...
-Wushu
Offense...
-Eskrima

The only ones I would actively pursue though would be the "Fun" ones.

Ever since i was young, i've always been interested in Karate. It mainly originated from Jin Kazama in Tekken 4 and i've been in love with ever since (even though his stlye is a little different.)

More than anything, I have always been a huge fan of boxing, real boxing mind you. People always seems to underestimate the true power of real boxing, thinking its a art made only to fight against other boxers, when it actually has ways to fight against other martial arts as well.

Din Mak- The so called Death Touch
or Jeet Kun Do

Weapons based included- I'd like to cover Filipino and Korean weapons- especially stick & knife/bladed weapons. Especially Filipino stick- that stuff is crazy IMO

Wing Chun. I've been doing it for 3 1/2 years. Though I had to stop. Mainly because of money reasons. I love wing chun because it gets straight to the point. BEAT YOUR OPPONENT AS FAST AS POSSIBLE. Also it was designed by women to protect themselves.

Either Modern Ninjutsu, Jeet Kune Do or Kali/Eskrima

I'm currently learning Yoseikan Aiki JuJutsu and Hokushi Ko Ryu JuJutsu.
Although my efficiency in either of them is only at 4th and 3rd KYU level, I also help my Sensei to teach the younger ones (children from 4 to 13). I must say that any sort of martial art (or any sport for that matter) is good for both the physical state of ones body and uplifting ones mentality. Although that being said, any experience being used for the wrong causes is pure violence.
Keep it as a sport or as a last sort of defense!

Best of regards for my fellow martial artists and fakku members!

Id master Street Fighting... I've been meditating to try and garner Ki to create a Hadouken but its harder than it looks!

Think i'll stick with the tried and tested Tiger Upper instead.

Kendo, Muy Thai and Wing Chun. All three are very badass!

Hokuto Shinken. Enough said

Krav Maga, without a doubt. It has by far the most pragmatic techniques I've ever seen, allowing a person to handily take down unarmed and even armed attacker(s). While I did some Taekwondo as a kid, I ended up being much better at boxing which my Dad taught me throughout high school along with some grappling and grab counters.

Russian Systema.

I would master Resshūken. ;)

I already do Iaido and Kendo, and know that I'll never master either, so... those ones.