As for me, my favorite ERC-721 token is CryptoKitties. This is because, I can breed my own kittens which live on the Ethereum blockchain virtually forever. In some cases, I get rare breeds which could become very valuable in the long term if sold for ETH.
All ERC-721 tokens are like that. Once you receive an ERC-721 token, it is there on the Ethereum blockchain forever.
I don´t think those kitties will be long term valuable.... they were valuable only when it was released, now the prices are just down AFAIK. There is no reason to pay a high amount of money on those kitties.