Spanish, Japanese or Mandarin Chinese... If you're going for full literary education, then Spanish is by far the easiest. If learning to mainly converse is the aim, I'd personally go for Japanese.
I was kind of in your shoes a while back, and I personally chose German. My reason is that I've always liked Germany as a country, and the fact that German is also used in Switzerland and Austria. Oh, and Die deutsche Fußballnationalmannschaft!!!
I also know Russian and can vouch for that. It's a really beautiful language with one of the best collections of writers and poets throughout history. But, like your other two aforementioned choices, Russian does not use the Latin alphabet. But on the bright side, at least it does use an alphabet! ;)
