regmapaure - congrats on your admits! It is good you are doing your research. The international rankings are indeed sometimes not very transparent and confusing since international schools don't often release their stats and rankings, as the result, have to deal with that void and rank schools based on information they can gather, trust, and make comparable.
However, you can usually get a glimpse of reality by checking the class profile and comparing average GMAT scores, and things like that. The more competitive the school the higher average GMAT Score it will have for example (the only exception I can think of is IMD). Anyway, another place to research would be the
Business School Reviews:
https://gmatclub.com/reviews/business_school/oxford-25 vs.
https://gmatclub.com/reviews/business_school/ie-68Oxford has had some growing pains - it is a fairly young program with a very strong umbrella name, and the program has not been meeting its high brand name expectations. On the other hand IE, has been fairly highly rated for quite a while and attracts a certain caliber of folks.
https://gmatclub.com/forum/said-211/dec ... acker.html (scroll to bottom)
https://gmatclub.com/forum/ie-mba-223/d ... acker.html (scroll to bottom)
I would also troll some of the employment report (again look at them with some eye for folks from your country - if you are from Latin America for example, what did most folks do from LATAM? Or if you are from Asia, did most folks stay in EU, move to US, or go back to Asia?)
Finally, I would get in touch through your network with current students at either program (and you also can ask the AdCom for their recommendation but I would find someone through LinkedIn or your friends). Ultimately, a big part of the MBA value is placement help and that's what you want to research with current students and recent alums.
Also, a big part is what and where you want to do after you graduate. Being in UK vs. Spain is different in terms of Work permits, employment opportunities (few are in Spain proper) and your language skills - e.g. if you don't know French, you probably have a harder time recruiting in France, whichever school you go for.