This is the only one I'm still interested in, and the only one I hold. When you transfer it around between your wallets and exchange it feels like "Yes, this is what I thought BTC would be". It's significantly more eco-friendly and actually a really interesting concept in how it works: https://docs.nano.org/whitepaper/english/

Needs more adoption from the mainstream crypto payment providers though. Honestly I suspect half the reason support is lacking is because nobody actually understands how it works (because it is quite different).