If you search the archives here in this forum and others, you will find a wealth of information and opinions about online certifications and TESOL or TESOFL schools. But basically I think you're on the right track; you're asking for advice and hoping to make an informed decision - the sign of a wise person.

As you are no doubt aware, the fact that EFL and ESL schools have become highly profitable businesses has been the catalyst to the birth of many training centers for teachers. My personal opinion is that very few of them are worth any of your time and effort; therefore, if it were I that had to make the choice, I would probably narrow that choice down to those who have proven themselves to be highly reputable and who are in some way associated with well established colleges or universities.

Also, remember, "buy cheap, get cheap." And, if they are offering what at first blush seems like an easy path toward your certificate - it probably is too easy; meaning that ultimately you'll regret not having received more thorough training.

Good luck - hope it works out for you.