When English speakers choose their L2, French and Spanish are usually on the table. Personally, I believe that Spanish is more useful language to learn as second foreign language. I feel this way for two reasons, which I explore in this essay.
First of all, Spanish has more people using it as their primary language, and total speakers too. There are roughly 470 million people who has Spanish as their primary language and 560 million total speakers, while there are only 80 million people who has French as their primary language and 220 total speakers. Statistically, It is more likely that you meet someone who use Spanish than some who speak in French.
Secondly, Spanish is an easier language to learn. It is very hard to master French pronunciation than Spanish because of the "r" sound. There are many people who have been speaking French as a second language, but still have difficulty speaking with a native accent. Moreover, If you are based on USA now, you can easily find native speakers who can help you practicing that language, and practicing with natives will accelerate your language learning significantly.
In conclusion, I am the opinion of that Spanish is the better choice to learn than French. This is because it is more widely used language, and because you can easily learn it than French.