Hi Fiona! I'm researching these certification programs as well. From what I've researched so far, CELTA is seen as the most widely recognized program. However, the TEFL/TESOL programs are widely accepted as well. From what I've read the main qualifications employers look for in TEFL/TESOL is that there are at least 100-120 hours as well as at least 6 supervised training hours.
I researched the CELTA also however it only trains you to teach adults and I want to be able to teach all ages, so I'm probably going to go with one of the TEFL/TESOL programs. The reason why CELTA is so popular is not just because it's Cambridge but also it's standardized. Employers know exactly what the program entails, whereas with TEFL certifications they can vary from program to program. But from what I've seen there are some very good TEFL/TESOL programs as well. Try going to the site www.teflprogram.com, they give some checklists when considering these options. Good luck!