Which of these languages...

is the most worth learning, in your opinion, and why?

Russian, Turkish, Urdu, Punjabi, Korean, Hindi, Arabic, Chinese, Bengali.

Additionally, which countries that speak these languages are pleasant and which are shitty?

Chinese has the best literature in terms of classical stuff and Russian best when it comes to more modern stuff. Hindi is the most spoken Indian and (I think) the one most connected to Sanskrit, which is what all that classical Indian literature was written in. Arabic has a lot of really brilliant old poetry.

All of them are nice and different to American culture, with Russian a bit less so, and all of them could be worth learning for more practical reasons. I would go for one of those four, in the order I mentioned them. (Actually I am learning Chinese.) Also, that is actually the reverse order of what I would consider the pure aesthetic beauty of the literature, a bit different to its overall stature - I think Chinese classics are incredible but not necessarily so beautiful, maybe just because China and Chinese really are so different. This is a pointless and no doubt quite personal observation though, so just ignore my rambling...

I don't know much about Turkish or so much about the other Indian languages. Korean is useful in one small country, doesn't have so much literature, and is fucking annoying - I started learning it and gave up.