[sp332]

The Lightning network is an overloy network on Bitcoin that allows faster transactions and higher transactions-per-second. Due to the economics of mining, it won't decrease the overall electricity usage of the network, but will make it more "efficient" per-transaction.

Ethereum is more programmable, to the point of being quite easy to shoot oneself in the foot. (Bitcoin is intentionally not Turing-complete to avoid abuse.)

Anything with proof-of-stake instead of proof-of-work is going to be less wasteful in terms of electricity. Ethereum is trying to get there but it has been delayed a lot.

The slow pace of block creation has been a problem with Bitcoin for a long time and lots of blockchains have higher transaction-per-second capacities and quicker verification times. Ripple was promising but had some serious scandals and I don't know if it has a future. Anyway, Bitcoin is one of the slowest ones out there now.

Several have improved on the privacy/anonymity aspects. The most famous of those I think is Monero.