To the tourists, Tainan’s most famous beef soup is the “WenZhang beef soup” and “Six Thousand beef soup”, but they are definitely not the two that locals will eat. Every Tainan people has a beef soup restaurant that they are used to eating.
The reason I didn’t recommend these two is that the WenZhang is too far away from Tainan Station, and Six Thousand you must get up at 5 am to line up, but believe me that A-Yi Beef Soup will not let you down.