For stability of coins, you can go through coinmarketcap and there's detailed information about the same. In my view Monero seems more stable. Ethereum almost doubled in this week
ETH is really usable altcoin because it is using when we are converting our tokens to btc and it is really helpful for those who make tradings every day, and it is also like btc, easy to use and understand. In my opinion, ETH is the mother of altcoins. Maybe for others, it is not, but for me, it is the number 1 coin of all altcoin.