The most important thing to consider when choosing a TEFL course is whether or not it is externally validated. Check whether they are validated by a body such as Trinity, SIT or UCLES. If this is the case, then a certificate course is a certificate course wherever you do it. They should all be recognised in Spain, especially if you get a good grade.
If you're looking for work in Spain, it might be preferable for you to do your course there. Training centres often have contacts with local schools and can provide valuable assistance in finding work. Check this out before you register. When you're on the course, you'll also build up a social network of teachers who will be able to inform you about which schools are recruiting and their reputations, etc. This again could influence your choice.
See also my answer to Arun and check out the FAQ's at the following link: