Hi, and welcome to the forum.

I'm not sure if Mexican citizenship will get you around the Spanish visa requirements, but as a fellow accountant, I can tell you that a few years experience in the US would probably yield big returns in the job hunt in Spain. Experienced accountants with US training are in demand in lots of international companies - and the fact of having more than one language is definitely a plus.

Fresh out of school you're not nearly as interesting, as there are plenty of new graduates out looking for jobs. But with a few "war stories" to tell...
Cheers,
Bev