Hi there,
I got my MBA at Northwestern and attended IESE on exchange for one quarter. Of the MBAs in Spain, I believe that IESE is, by far, the one with the best reputation as well as the one with the best prepared and most international student body.
It was co-founded in the 1950's by Harvard and Universidad de Navarra (a private university run by Opus Dei, although no religion included in the MBA!). So, it was modeled after Harvard and uses the same methods.
IE is getting to be quite well respected. However, keep in mind that it is just a one year program. Probably fine if you are sure you'll be wanting to stay in Spain, but not as well known outside of Spain.
Esade is better known for the undergraduate program.
After working here in the financial sector (in Madrid) for the past 10 years, I can say that IESE has by far the best reputaton and it would probably be easier to find a job after that program (although the other two are respected they don't have the same network of alumnae, etc.)
Good luck!