ease (Score 1)

It's probably been said in here, but if you don't have a strong motivation toward a particular language, choose what's easiest. Whatever you choose will be useful.

Because learning a new language is difficult, it's usually overlooked how much they differ in complexity and difficulty. My ranking, complex to simple:
Russian (miserable)
German
Spanish, French
Japanese
Chinese

Drawback with Chinese is that the sounds and vocabulary are completely foreign. Japanese has imported a fair amount of English, which helps. And Spanish and French each have a lot of hooks for English speakers. (German too, but I find it more opaque.)

Chinese or Japanese are both good choices, but I'd go with Spanish. It's the de-facto second language of the US, and really the first language of this hemisphere. It opens your home up in new ways.