Long ago when someone was ready to study a martial art, they would seek out a particular teacher or Sensei. Where the dojo was located was irrelevant. If they had to travel long distances or even move to study under this person, they would. Today people choose martial art schools for convenience and affordability. The Sensei doesn't seem to matter anymore. This is a mistake.
The Sensei - student relationship still does exists. It is however just as hard to find it today as it was long ago. If you join a commercial martial art school that has 100's of students, how can you expect to learn anything from the Sensei on a personal level? The school becomes a factory designed to simply make money. It is a vicious cycle. The bigger the school, the more space needed, the more the overhead, the more more students are needed. It becomes very impersonal.
The interaction between the Sensei and the student is perhaps the most important part of the training. This relationship grows over time. Many young students today make statements like "Take what is useful and discard the rest and then move on". Aside from being extremely disrespectful, what makes the young student think that he or she is even going to recognize what is useful or not? Pure arrogance? It doesn't work this way. What you wind up with is a generation of students that jump around from one martial art to the next, never fully learning or accomplishing anything. This is how martial arts are ultimately destroyed.
No matter which martial art you choose, you must first consider the Sensei. It doesn't matter what the school looks like, it doesn't matter where the school is, if the Sensei is competent and takes an interest in you, then you will learn something. If not, well then you might as well join an aerobics center.