If you are thinking about whether or not to become qualifed as an EFL teacher, you might benefit from reading this TEFL careers advice or advice from the British government.
As both articles suggest, the range of courses on offer can be bewildering. However, in my opinion one major deciding factor for choosing a course should be how much extra value the course will add to your employability as a teacher. Investing in your future is always a good thing, but like all investments some are far better than others. Along with a willing-to-learn attitude, teaching practice or experience are probably the two most important attributes that employers look for when hiring new teachers. If the course you are considering does not involve any real, practical, hands-on teaching with relevant and worthwhile feedback, you will not be as compettitive in the recruitment process as the other applicants who do have that.
On-line, distance learning can be a good thing, but it very much depends on the type and purpose of learning. If your goal in taking a TEFL course, such as the CELTA, is to show that you are a competent teacher, the course needs to have a practical teaching element.