This is an excellent comparison of the main features of Cardano (ADA), Ethereum (ETH) and Bitcoin (BTC) that shows exactly how much more energy efficient Cardano is.
Sure, some may call it cherrypicking, but there is a very strong case for Cardano when it comes to energy efficiency. Proof of Stake is a much more eco-friendly methodology than Proof of Work.
Transaction fees are also incredibly low, and should remain negligible with higher transactions thanks to more nodes coming online.
Support for Smart Contracts is already available in Ethereum, but given how well the Cardano team is sticking to its release timeline, we should see it for ADA very soon.
As for Bitcoin, it fails in all technical areas, but will remain the leading crypto for the foreseeable future, given its momentum. It is not going anywhere, and will transform into a store of value, rather than a digital currency that you use for everyday transactions.