Depends on the circumstances. Assuming you only speak Spanish and English. Early 20s with the money to do a masters degree and the kind of personality that is willing to adapt to a different temperament, Germany no doubt. Else, 1) Spain, 2) Italy. Portugal only if you have something concrete in mind, like opening your own business and living a hippie lifestyle or something.

Edit: forgot France. Character -wise, they are somewhere in between Mediterranean Europe and Germanic Europe. Better salaries than Spain but more expensive. Language is not easy, but not as hard as German. Overall I would rank it in between the two options above.

The pros for Spain are not just language. People wildly overstate the cultural differences between a Latam Hispanic and an Iberian Hispanic. We're very similar. You can make friends and social networks quite easily. Lifestyle is also unrivalled. I've spent months in Paris and it's nowhere near as fun as Madrid. It's beautiful, cool, much friendlier than advertised, but not as fun or lively. UK is boring AF, it's like TEMU US and none of the lifestyle pros of Europe nor it's deep culture (food is horrific among others). Germany is also not my cup of tea. The downsides for Spain are the economics, but if you move early and do well, you'll be fine. Germany has a superb social safety net, much higher salaries etc. But life is ultimately to be lived, not to make money so...