The research you have done is correct: the CELTA is the most highly regarded.
In answer to your question, think about it from another point of view. If you wanted to get your hair cut or your car repaired, would you prefer someone with a qualification or someone who did the job for five weeks in Sri Lanka?
Of course, some students and schools will be happy with a teacher without teaching qualifications. It always comes down to that choice. Your choice is: do you want to work in that type of school, with that type of student? I'd say that if you want to make a career out of TEFL, a serious qualification is essential. If you don't want to make a career out of it, then that's a different matter.