Sorry if this has been asked a thousand times before, but I've been trying to find the answer to this for a couple of hours now, and my brain feels like it's melting out of my ears. :)

Is there much difference between TEFL, CELTA and TESOL qualifications, both in the sense of "material taught" and "inherent employability"? I want to be sure that I'm not spending money on a useless course.

Thanks!