There are few cryptocurrencies other than bitcoin that will be Monero, Ethereum, Litecoin and so is preferable for me.
For me, definitely the most important coin (excluding Bitcoin) is Ethereum.
In 2021, Ethereum plans to change its current consensus algorithm for Proof of Work to Proof of Stake. This move will allow the cryptocurrency network to operate on its own with much less energy, as well as with an improved transaction speed. This will allow the participants in the network to "bet" their etherium to the network itself. This process will help secure the network and process any transactions that occur. In addition, anyone who uses the feature will be rewarded with a cryptocurrency, based on an interest rate model. This is an alternative to the bitcoin proof mechanism, in which miners receive more bitcoins to process transactions.