Nano is fast and free because it is not used much. How many transactions per seconds did they achieve? I think it was in the ballpark of a 100, much too low for a global currency. Let's say 10% of the earth population want to use nano once a week. Then you need 0.1×8e9/(7×24×60×60)~1000tps. Then it might replace paypal, but not cash or card, and the microtransaction usecase is even farther away. Indeed it seems better than bitcoin, but that's a low bar by now. I do like nano's idea of voting weight delegation, it seems like an elegant solution to keep the power over the system in the hand of the user/owners.

At the moment I feel a centralized privacy coin would work best for me. Centralization brings performance and the private part avoids excluding participants.