Congratulations on deciding to learn a second language. The United States has, for decades, lagged behind other nations in our knowledge of foreign languages. (In China and Japan, English is part of the core curriculum in secondary schools; and in Australia, one out of four students studies an Asian language.)
How do you decide which language is for you?
First, give some thought to which second language might be most useful to you as an adult. Obviously, the demand for Americans who speak Spanish is likely to keep increasing in most fields. Do you see yourself working in a career where knowing Spanish might help you? Or do you aspire to work in international business or for the government with another specific nation or culture, like, for example, France? If so, then French is the logical choice. Many other international business students choose to learn Chinese (Mandarin), Japanese, Russian, Arabic, or Farsi because these are some of the languages spoken in countries leading the world's business community. Many people entering medical professions choose to study Latin because so many terms for various aspects of human biology, anatomy, and immunology derive from it. What are your interests and how would knowing each language help you reach your long-term goals?
Also ask yourself how much you want to be challenged by learning a second language. For example, conventional wisdom says Russian and Chinese are historically difficult for English-speaking people to learn; and while German is still fairly difficult, French and Italian are less so, and Spanish is simplest for an English speaker to learn. What other reasons might sway your choice? If your ancestors are from France, you just might enjoy learning French more than Spanish, with which you feel no cultural alliance.
Whichever you choose, good luck! I mean buena suerte (Spanish), or would that be bonne chance (French)?