In an interview with bloomberg (https://www.bloomberg.com/news/videos/2017-12-07/coinbase-ce...), he didn't say that he thinks Eth is better but it's obvious that they are more bullish towards Eth. They have also built Toshi, a Dapp store for Eth.
Coinbase has become a giant on the back of the work of Bitcoin Core developers and will continue to do so however, they have given NOTHING back to Bitcoin Core. Not a single BIP, they don't sponsor any core developers and they are not helping at all with Lightening Network.
It's very easy for them to sit back and complain about the state of Bitcoin, but Bitcoin is an open source project and they have the money to invest some money into Bitcoin core to improve it. But they rather prefer to pump shit coins and engage in insider trading. In my opinion Armstrong doesn't care about Bitcoin, they are short sighted and don't believe in the long term vision of Bitcoin.