One style is not "better" than the other. The two styles complement each other, and ideally, a student should study both to keep his or her internal and external aspects in balance. Both styles will increase flexibility and balance and also help relieve stress. Both styles are also demanding, though in different ways. Generally speaking, you may enjoy Shao Lin more if you are looking for a more aerobic workout with self-defense applications, emphasizing speed and power. Tai Chi may be appropriate for you if you want to improve your mental focus or if you are looking for a regular workout that is less strenuous.