＜Which is better for you? Large or small institute?＞
In general, you will teach what you’re told to teach, so you don’t have to prepare lesson plans for each class in large EIKAIWA. Smaller schools are often more flexible with their curriculum.
Large EIKAIWA usually have textbooks and other lesson materials for the students as well as teaching manuals for the teachers. This is a huge relief for new teachers with no/limited previous teaching experience. You will teach what you’re told to teach, so you don’t have to prepare lesson plans for each class.
Not getting paid for the time spent making lesson plans either during periods between classes or at home, is a common complaint from teachers, so large EIKAIWA that have the lessons plans ready for you can be very attractive.
However, if you're the type that needs to express creativity in teaching methods etc., you might feel over-controlled working for large EIKAIWA.
Smaller English schools are often more flexible with their curriculum. Not having curriculums already prepared and leaving all the responsibilities to teachers is not uncommon.
Teachers plan their own lessons, sometimes even choose lesson materials.
You have a lot of freedom to experiment, and ultimately it may make you a better teacher.