I think Ethereum is the most stable. Although it has lost in price in last days, it's temporary I think. The main reason why Ethereum is stable is that it has a person behind it. I'm sure that Buterin will support Ethereum in case something happens with the market.
Right, Buterin is important factor to support ethereum but most important reason why it will be even more stable is that's popularity. Every day there is new project is appearing that uses ehter infrastructure.