QTUM
This is one of the most promising contenders along with others too.
This is a hybrid Cryptocurrency technology that takes the best skills of both Bitcoin and Ethereum together already, even before blending together.
The level of Abstract Accounting layer that it possses gives the QTUM's Blockchain Smart contract functionality also.
I went to get my little research on qtum and I want you ask you a question
What relationship does qtum has with Bitcoin and ethereum and is it built on both ethereum and Bitcoin blockchain?