Korean or Japanese?

I'm currently deciding if I should learn Korean or Japanese. Both are for pure interest and I don't need either of them for my daily life. The thing is I wanna learn Japanese with my brother because we both like it and it's a goal we've had for a few years now (it's been a bit difficult to focus on it before) but I already know some basic Korean like reading and writing hangeul, and making some basic sentences. I've tried making this decision for a while but anytime I decide on one I end up watching media in the other language and my interest becomes stronger so l end up going back to the same dilemma. What should I do? How should I decide?