Welcome to MT, good to have you with us---and so far as your hamstrings are concerned, you're gonna wind up doing a fair amount of stretching to untighten them, no matter which one you choose. Starting a stretching program right now would actually be a good idea, so that when you actually pick an art and start attending classes you'll be up to speed.
As far as which are to choose, that depends on a lot of factors, as Terry pointed out. Check out the threads Kacey pointed you to for starters. There are a lot of different issues that you should probably sort out: your main objective in MA; whether you are looking for a striking art, grappling art, versatile mix (such as Hapkido); hard or soft style; more emphasis on kicks vs. less, and so on and on and on.... I would suggest visiting a number of schools, to see as many different MAs as you can in action, and keep track of which ones kick the gong for you. A lot of times, people see an art being practiced and know that that's the one for them (or, conversely, that it's definitely not for them)...
