All things considered, I think I'd rather study Spanish. It'd serve as a great gateway into Romance languages, and fluency would give me access to almost the entire Western Hemisphere.
By my mark, Esperanto is a fun experiment, but like most conlangs it'll probably stay like that. Lingua Franca and pidgins develop naturally, usually through some sort of necessity. And in a world where most educated people speak English, it's rather hard to warrant learning an entirely new language for the sake of universal communication.
As a sidenote however, I do like the fact that the Esperanto word for "nonsense" and "gibberish" is volapukaĵo, referencing its rival conlang, Volapuk. Way to be subtle there, guys.