To all intents and purposes
TEFL =
TESOL in terms of qualifications. A basic first job will usually require a degree and a
TEFL certificate.
The
CELTA is, in my opinion, a top end
TEFL certificate. It is perhaps the most widely regarded. It is, however, a very intensive course and I believe it's best to have a couple of years experience before taking it.
What a lot of people do is take a simple
TEFL certificate, teach for a while and then, if they decide they want to advance to DoS positions or higher up the chain they take a
CELTA.