Quality of training and classes in Taiwan can run from downright shoddy to decent quality. In some ways you get what you pay for, some local shops will offer low prices and stuff classes with large number of students. Smaller classes are better, ideally get trained in classes of 4 or smaller.
Assume being a foreigner you would be best off with one of the native English instructors on the island, far easier to communicate and understand, you can find a few listed on this site.
Depending where you are, doing your open water certification up in Taipei is convenient. Once you get on to AOW I would always recommend doing that down south or on one of the islands so you get chance to do some boat dives.