I think the recent "crypto kitties" issues highlighted some of the scaling concerns of the Ethereum "virtual machine".

Ripple is centralized and can be argued is not even a blockchain.

Litecoin is fast AF but its the "younger sibling" of Bitcoin.

One to keep an eye on in 2018 in Cardano here's the introductory whiteboard talk https://www.youtube.com/watch?v=Ja9D0kpksxw