Well it really depends were you live, because on the long run you will learn the language you choose. But it really depends on your geographical situation. If you live in the south probably spanish is for you. If you're up north well le français c'est pour toi ;)
Definitely not Japanese for a native English speaker. Probably Spanish would be easiest, but French is also good. Try out Spanish and French and see which is easiest for you. If I were you I would learn Spanish, because Spanish is spoken a lot in the US.
Spanish would be good for you especially since you live in the States. Not only will it be beneficial to communicate with Latinos around you but it gives you great job opportunities where Spanish speaking individuals are needed