Interesting question. I think the easiest would be to learn Spanish if you are in the USA. Considering there are millions of hispanics in America (and Spanish speakers around the world), it is a language that could help you to approach them in their own language. Spanish is an "easy" language to learn, grammar is mostly the same as in English and all you have to do is learn vocabulary once you learn how a sentence is formed. If you speak Spanish fluently, you could easily understand Portuguese and Italian too, and they would understand you.
But I would not discard learning Chinese, I would love to speak Chinese, but I think it takes a lot more time and dedication than learning Spanish.
The question is how much time are you planning to dedicate to learn a new languague.
I am Mexican, and speak English (I learned it at school) and German (I learned it by my own), and a little bit of French...of course Spanish too.
My recommendation would be: If you have the time, learn Chinese, I believe there are millions of business opportunities there and they will increase every year. If you are not planning to dedicate years of study to learn a new language and need a short-term foreign language skill, then learn Spanish.
Or..you could start with Spanish and then see how it goes, and go for your third language.
Once you learn a second language, the third one becomes a lot much easier to learn.
learn Chinese
Learning mandarin would be a very strong asset for business. It will be ever so useful when it comes to communicating overseas.
Chinese is good, but check out French.
Spanish and Vietnamese !!! :) trust me
I am a 2nd year collage student and i am majoring in business. I want to move to the city and do sales and marketing or something with a business. I am learning spanish but i was wondering if it would be very useful to learn Chinese or something so communicate easily with oversea deals and stuff.