European Spanish, European Portuguese, Argentine Spanish, Brazilian Portuguese ?

Well, in general I think that Spanish would be more useful. With that said, both are pretty similar. I mean, I speak Latin American Spanish and can perfectly understand somebody who speaks Spanish from Spain. There are only differences in a pronunciation of the "c" and "z" sounds. There are also differences in vocabulary, however that happens with different countries of Latin America as well. I don't think it really matters which you learn because you will be understood either way. Don't try learning a certain style, such as Argentinian or Chilean Spanish just yet, wait until you have the basics that every country uses first. Good luck!