English is the world's current Lingua Franca.  Any continent you go, you will find a good number of people who speak/understand it.  It might not have the most numbers of speakers, but I'd bet if I was speaking any other language in the world, and wanted to learn a 2nd to help me out, English would be the one that would help me most.
As someone who speaks English for a native tongue, I chose to study German.  I figured for what I wanted to do, Spanish would be completely useless.  All the Spanish speaking peoples I'd be interacting with would already know English for the reasons outlined in my first paragraph, and I don't plan on interacting too much with those who don't.
I guess I'll just end by saying Spanish is a very pretty language, as is Polish.