for the most challenge, russian. you also get to read pushkin, tolstoy, and dostoyevski in their original. russian is also good for involvement with the russian mafia or for ordering a russian bride. for the most prestige, go with french (literary) or german (philosophy). german also adds a bit of depth because it's not only prestigious in philosophy circles, but it's big in industry and it's far more challenging than french. for diplomacy/military or international politics russian or arabic (but mostly arabic these days). for the future (commerce,politics,communicating with your new rulers, etc.), mandarin chinese is best. for something a little different and for commerce japanese. japanese is also good for belonging to odd japanese subcultures (harajuku, cosplay, manga, futurani, hentai, loli etc.) for the most utility within the united states, spanish. of course it goes without saying that plans for latin america would also benefit from spanish. p.s. you should be aware that the women in spain are EXTREMELY hot. and that learning arabic will NEVER get you laid. it will, however always thrust you into odd and uncomfortable conversations with arab men. good luck

Chinese will probably be the most useful but also most difficult, I'd say spanish

Take Chinese. We're all going to have to learn it soon anyway.

If I lived in Texas I would commit myself to spanish.

Russian....that's a good language to know for business...as is Chinese. Most Germans, Japanese, Spanish and French speak English already.

Surely Spanish is the one you would have the most practical use for, living so close to Mexico. It's also the easiest one to learn of those you mentioned.

Whichever nationality of women you prefer.