Boy, I don’t think there really is a good answer to this one. I have found it VERY much depends on the type of person you are as well as your physical attributes. When I started in Martial Arts, I started in Shotokan which is a very traditional, deep stanced technique. I’m 6’3 and about 240 pounds, and when I do anything I learned from Shotakun at my current mass, I find it very difficult to maintain the stances for long periods. I then moved to Shoran Ryu, which is very light footed, quick striking and (I feel) milder technique on my body. The best thing I can suggest to you is to try looking at all the Dojos in your area and ask about maybe sitting in on a class just to get a look at the stances they use and see how it reacts to your body. I personally believe that Martial Arts are kind of like wearing clothes, you have to find the right style and fit that works for you.

Many martial arts have their own set of techniques and approaches for balance and flexibility. However it all falls back on the same keys. The ones that have stood out in my experience have been: strength and relaxation. The relaxation helps you isolate the muscle groups that will need to be active when you're stretching. That way you can develop the flexibility in the other muscles without your own body working against you. Yoga works very well in this regard. However flexibility is one item that takes a lot of time and constant vigilence. The strength helps you activate the muscles that need to work overtime to pull your body into the stretch. It doesn't help to have flexible muscles if you can't move that part of your body to its full extent. The strength also seems to cut back on chances of a nasty charlie-horse. Focused weight-training can help quite a bit in this department. Balance is a matter of feel but the best advice I can give you is bend your knees. It's an easy aspect work at least! I find myself standing on one leg in grocery store lines or around the office. If someone notices they might raise a curious eyebrow but it's not too weird to be not worth the practice time. (In my opinion anyway.) Tai Chi has a number of good balance-focused drills like push hands along with many of their slower techniques that stress control and balance. Wing Chun Kung Fu's chi sow can be helpful if done with foot work. Overall, foot work can make dramatic differences in your balance and it's one item that many styles don't stress nearly enough. Overall these items can be found it almost every martial arts style; each stressed to different degrees. Good luck finding the right match for you. Don't get locked into a specific style or technique and the keys for you will become apparent in time.

From my 10+ years of experience, if you are wanting to become flexible and learn to keep yourself safe, I'd study one of the following, 1. Hung gar kung fu 2. Muay thai 3. Ninpo-taijutsu 4. Tai chi The main thing is, be stretching!! Every day, 3 times a day, not too hard, not too soft, and make it a part of your life. Any martial art benefits from flexibility, so pick one you like for self defense purposes, then make it a personal effort to reaching a goal. Polish yourself, don't rely on anything but your own hard work! Thats what Kung fu means :P No matter what you decide, just know that it is entirely up to you what you become. don't get too caught up in the pizazz of modern martial arts trends, and remember they exist to >polish and refine< you. Not make you.

... I also suggest Wing Chun, Tai Chi & Tai Chi Chuan, and Ninjitsu ... since I do not know ALL martial arts, I am not sure if the above mix would be "best" or not, but it is most definitely functionally adequate enough ...