Currrently my two favorites are Siacoin and Pascalcoin.
The reason for their stability is that Siacoin has a real and working product and Pascal is an innovative idea, which is its own blockchain, using account names that are distinct from the pascal blockchain to ensure only the last 100 blocks are needed. Ensuring the speed, cost, and longevity of its blockchain. Other blockchains have to consider the entirety of every transaction that ever occurred, meaning larger blocks, leading to longer transaction times and higher costs.