First of all congratulations on getting multiple admits. I got an admit from ESADE and other schools so i ended up picking another school. Hence, I cannot give an expert opinion on ESADE. But from what I heard through my interactions with the previous cohort of ESADE, its a good school, reputed in the business world for years (one way to cross-check this fact is to see its FT rank over the past 10 years). Secondly, if you already made up your mind in staying in the EU, then its better to get your degree from the same place where your school will be most recognized (not saying that Boston would not be recognized just that recruiters at EU would be able to do an apple to apple comparison if you do it in the EU). Thirdly, keeping in mind your post MBA goal, Spain especially Barcelona has a well-renowned start-up culture, even if you cannot crack a role in VC (which is difficult but not impossible and your start-up exposure can be used to your advantage), you can make your way to one of the start-ups in Barcelona. Fourthly, I do understand your concern about funding but while considering a B-school you should treat it like a long term investment-this is what makes people invest over 150K in the Ivy league schools and they reap the returns over the long run. So, BU scholarship might appeal to you now, but think of what you'll get out of the school after you graduate? And if you're too keen on the budget factor then you can accept the BU offer and try and network your way to EU.
I can give you two suggestions: Try to negotiate your way through the recruitment desk at ESADE. Securing admits from higher ranked schools might help you with this (you need to make the recruiter feel how big a loss it would be if you end up rejecting their offer). They offer need based scholarships too and i believe, you're not too late for it. Hope you end up making the right choice. Cheers!