Nothing is as frustrating as being in a Japanese class for passing the JLPT examination, while your fellow learners are just taking the course for general interest. The pace will be too slow for you and the lessons not really targeted. People learn Japanese for different reasons. For the best result, make sure you join a course that fits your purpose.
Purpose #1: Passing a test. You may need get JLPT or other certification for visa purposes or university admission. Most Japanese schools offer specific preparation courses for this, which will help you get familiar with the test format. Moreover, you will be in a class with people motivated by the same purpose.
Purpose #2: Cultural interest. You may have visited Japan or seen much about it on tv and want to know more about the culture. You like manga. Maybe you even met a Japanese partner and want to be able to communicate with him/her in the native language. Learning Japanese is definitely a good idea to increase your cultural understanding.
If a cultural interest is your purpose of learning, choose a class that offers cultural exposure on top of the usual language teaching. Your interest may fade if you are simply single mindedly learning vocabulary and grammar.
Purpose #3: Business. If you are going to do business in Japan or work with Japanese, it will help you greatly if you can speak their language. A common challenge for business Japanese learners is combining the lessons with an already stressful job.
Most Japanese schools in Singapore offer business Japanese courses. These courses may require prior knowledge; it’s rather hard to discuss contracts if you do not know how to say “hello”.
If time is an issue, consider private lessons; either in person or by signing up for an online plan that includes virtual coaching sessions. You definitely would want to squeeze as much business-relevant learning in little time, so be careful to choose a course that maximises your result.
What is the best course for you does not just depend on how good the school or teacher is. To make sure you get to learn what you want to learn, choose a the course that fits your purpose.