First, let us consider the self defense aspects. All martial arts can be effective, and so that is not a limiting factor. However, one might be more concerned regarding the ability to learn self defense quickly. To the extent you see a particular art and feel it fills the void, that approach may be best for you. Numerous arts work to develop one's confidence quickly in their ability to defend themselves as an expedient to ultimately lead the practitioner to develop positive character. If a particular art seems to speak to this need, it may be the best starting point. That said, as a caveat, one should note that the ability to defend oneself accrues most quickly to those who do not concern themselves with that aspect of training. Second, we can consider exercise. Some martial arts such as Tai Chi have specifically designed health benefits, and so those arts should be pursued to the extent of one's interest in them. Otherwise, all martial arts provide exercise and can be practiced vigorously to one's ability and interest. Most arts that emphasize striking employ katas as a training method, which can be practiced alone, while arts that focus on grappling or throwing an opponent emphasize practice between two or more partners which can be very aerobic. Again, all arts can be adjusted to one's limitations, and so the different approaches should not be seen as explicitly limiting factors.
Finally, we should consider personal growth, which affects effectiveness of the art over the long run. Martial arts training has two basic components: technique an understanding. The objective is to be effective in protecting oneself consistently in all situations, so both are required to accomplish this goal.
The need to train in technique is obvious. One trains to develop reflexes to protect themselves as the situation arises so one is not trying to figure out the footwork as the punch is coming.
The need for understanding is more subtle. A proper understanding of the principle ideas underlying an art help one to close openings so one cannot be countered and defeated while performing the techniques. Those who think a martial art is the techniques alone are in for a rude awakening when they discover that every technique can be countered. There is no perfect technique that can guaranty safety in all situations. The ability to close openings during any given technique is related to one's state of being more so than the specific technique chosen. A correct understanding leads to a correct state of being.
Any potential school should be evaluated in its ability to bring a student from point "A" to point "B," meaning how the school delivers on both basic components. How proficient is the instructor in technique and what are the training methods? Does the instructor have a correct understanding from the point of view of realization? If not, does he/she at least have a correct intellectual understanding? Are they sincere and have they developed positive character? Obviously, the feeling of comfort one has with a particular instructor would enter into this equation. Ultimately, the personal growth aspect of training is not a patchwork of unrelated terms reiterated due to the pleasing sounds and some vague notions that these ideas may be beneficial one day. This aspect of training is an integral part of the daily practice, and critical insofar as it is required to deliver truly effective self defense and health benefits. This aspect of training in a school should not be underestimated, and critical steps to avoid errors is the subject of the next article below.