Bitcoin Green (BITG) is The Ultimate King of sustainable cryptocurrencies in my opinion!

As it says: "Bitcoin Green is the global blockchain solution for sustainable cryptocurrency. It is founded on 'The Green Protocol,' which utilizes a highly efficient proof-of-stake consensus algorithm that solves many of Bitcoin’s sustainability and scalability problems. Bitcoin Green, the organization, aims to shed light on a number of critical issues facing proof-of-work based blockchains and raise public awareness for the environmental and economic problems arising from such issues."

I do not know any project more sustainable and green than Bitcoin Green. I'm happy to see other suggestions!