online courses are same to a book. better go to the offline courses (IMHO). 

It depends where you want to teach. You can get a job in parts of Asia with little or no qualification. Obviously the more training you have, the better chance you have of being a good teaching and finding better paid work.

The gold standard are the CELTA or TESOL courses, accredited by Camridge ESOL, or Trinity College. You can study these courses at centers all over the world, it's a month of full time training, or part time equivalent. It costs a few thousand.

From experience, if you are seeking work in Geneva, a number of the better schools will only accept CELTA. Speak to potential employers before committing to a course.

Hi,

I agree with some of the points above.  There is a distance mode TEFL course here http://www.teachenglish.co.uk/tefl-courses/certificate-level-courses/ofqual-accredited-certificate-in-tefl.html that is recognised/approved by the british government ( same as CELTA ).

The CELTA course is a real killer! One of my co-students was seen crying under the table during the lunch break, but if you can stay the course, then you are set fair for future employment. As one of the previous posters has mentioned, there are many schools in Switzerland who stipulate 'CELTA trained' so if you can achieve this qualification, then that is definitely the creme de la creme. Good luck!