I studied at NCKU for one year in 2001. I strongly suggest to take the one-on-one classes. They are not much more expensive than the group classes and you will get much more out of it.
The group classes are tought by the same teachers as the one-on-one’s; the teachers are mostly college students or college grads without formal teaching education. So, if you are unlucky your group class teacher will be teaching a group for the first time herself.
I took 80% one-on-one classes and they were very helpful, since I could set my own pace and I could take charge of the classes myself; this way you can get much out of classes even if the teacher is not so talented.
2 hours of one-on-one cost just around 500NT, which I think is a very good price (they raised it though). Chose “Practical audiovisual Chinese”, since this is the textbook most teachers are familiar with.
I do agree with littleiron that NCKU is not for advanced students, but up to high intermediate it is a very efficient learning environment (up to and incuding Audio-Visual volume 3; that is my own definition of high-intermediate though; the MTC places this book on mid-intermediate, but I think if you really finish this book from cover to cover, then you are pretty good).
You will do lots of talking, thus become fluent fairly quick. On the other hand, if you are more into classical Chinese, real literary Chinese or business Chinese, don’t chose NCKU. It is really more like a place where you learn Chinese to get along in Taiwan.
I have to admit that I have never been to another language school, so I am just judging from my own “satisfaction level”.
P.S.: I didn’t notice any particular rudeness in Tainan. Stares, pointing and an occasional “hello, how are you?” was all I had to put up with. Often people appeared to be very friendly and willing to help (once I was sitting on a bench all by myself waiting for a friend, when an old man came up to me and asked if there was a problem; kind of cute).