I have taught TESOL for numerous years and have a CELTA certificate. I also have a Master's Degree in ELL (ESL) I took the CELTA course and discovered it was wayyyy below my level and it caused me problems (along with me opening my mouth too much) as when the teachers asked questions I answered them and one teacher actually took exception to it as I used terminology wayyyy above her expertise which irritated her.

As for which one you want. Take the one you feel comfortable with. I mean if you are going to teach children take a TESOL course. If you are going to teach adults who have a grasp on the language a CELTA course is better If you plan to work for a British curriculum school take a CELTA.

I applied for an Australian language school once. My CV had me working 6 years in an ESL classroom I'm a licensed teacher from the USA. I have a M.ELL. I have a TESOL certificate.

I was denied the job because I didn't have a CELTA.

Think of it in those terms.

CELTA you will not learn grammar at all. SOme TESOL courses teach you past tenses (I don't know why), but at least look at the instructors and the curriculum. THis is major.

If you have other questions feel free to ask.