Not OP, but I've asked myself this as well. I think it depends on where you live and what you want out of your language learning experience. If your goal is to learn something more useful in everyday life and you live in the southern US, Spanish is a great option. If you're from Canada, French is probably the most useful. German and Mandarin are useful in the business world, but the latter is significantly harder to learn. If you're not worried about maximizing the utility of what you learn, Norwegian is considered one of the easiest languages for English speakers, and let's be real, Norway is awesome.
It's more important that you stick with whatever you choose though. That's the part I've struggled with.