I signed up for TEFL International after a year of teaching without a proper certificate. I had an online TESOL, but the top employers wouldn't recognize it. At the time, you had the choice between CELTA and TESOL here in HCMC.
I decided on TEFL International because it had the reputation of being the most supportive course in the city. I knew plenty of teachers who had taken a CELTA and said that it was like a military bootcamp. In contrast, everyone who had studied with TEFL International talked about how friendly and fun the trainers were. It was also noticeably cheaper while still being an internationally recognized certificate.