There are thousands of ESL teaching courses available, with all sorts of claims being made about them and accreditation that can be valid or bogus. One simple test is to look at adverts to see what employers are looking for, so I went through 200 adverts for basic teaching jobs around the world, and a few teaching online. I ignored managerial positions, university and specialist jobs. This does not rate the contents of courses, though it is clear which courses employers trust and prefer. Qualifications are given with the percentage of the teaching jobs advertised that a person could apply for.
You could apply to 100% of the jobs advertised with the CELTA.
Trinity College- 89%
The Trinity CertTESOL is almost universally recognised as being the equivalent of the CELTA, and many argue that it is better, but 11% of the job adverts surveyed only mentioned the CELTA. It is possible that you might get one of these jobs with the CertTESOL, but employers might really only want the CELTA, possibly down to snobbery or ignorance, and it is a buyer's market. It is the only other qualification that is regularly named, though I haven't seen any advert that only asks for it.
Or Equivalents- 78.5%
Courses that have over 100 hours of tuition (120 is a common figure) and several hours of observed teaching practice are generally regarded as equivalent, though the quality may vary according to the provider. Anything less than this is not equivalent despite what it might say on a website or in promotional materials.
Other ELT qualifications accepted- 37%
Courses that don't include teaching practice or that are shorter than the ones above but provide some certification would be OK for just over a third of jobs.
No teaching qualification required- 10%
Some adverts where no teaching qualification is required did specify that applicants had to be graduates.
I looked at 200 basic teaching job adverts on Tefl.com
- some of these were for multiple positions, but percentages are based on the numbers of adverts. This survey does not assess the pedagogical worth of a course, but it may give an idea of what employers want. CELTA and Trinity are the two courses that are repeatedly asked for by name- so far none of the equivalent courses has managed to make the leap into being name-checked. 2% of job adverts asked people with online courses not to apply- a small number, but the fact that they don't want the bother of throwing an application in the bin may be worth noting.
I have no involvement with or interest in any ELT training course.