OP listen to Looney. imo, his information is the most useful in this entire thread, especially if you're just starting.
make sure you visit the schools and watch a few classes so you can get a feel of the students, the atmosphere and most importantly the instructor. many places will offer a month to month membership so you can switch to another school later on.
imo, the most important thing is actually starting any martial art. once you become profficient, you will understand what you do or don't like about the particular style you've chosen and what you do or don't like about other styles. and even if you switch to another style later on, your previous experience will always be valuable in some way.
and all martial arts will get you in better shape, especially cardiovascular shape.