Learning languages

I really would like to start learning a new language. Four years in I have a good continuous improvement routine for Chinese. Some day, I want to be able to read real books and hold my own in a real conversation but that is still years away.

I have learned a lot about learning and I would like to put that into use. Should I pick a relatively low hanging fruit like Estonian or Danish or perhaps Russian? Or go with something useful but new like French? Or go after something classic like Greek or Latin? Or go obscure with a relatively uncommon choice like Armenian or Georgian? I am fascinated by writing systems and anything with non latin writing system would probably keep me interested.