For the long term I am sure that Ethereum is more promising than EOS, this is because there are hundreds of tokens that use ETH so that the future of ETH is better than EOS.
Without a doubt, ETH has hundreds of tokens developed on it. Its user base is much bigger and it’s highly flexible in development than EOS too. On the other hand, EOS is new with a small community and development team. However, it has promising technology that could rival Ethereum's tech in the future, if EOS gains mainstream adoption. Considering how popular smart contracts have become within the blockchain industry, there's a high probability that both ETH and EOS will survive for a long time.
The key indicators for the survival of any cryptocurrency is development, innovation, community support, and most of all, mainstream adoption. Until now, ETH and EOS have such indicators, which means that they will last for many generations. As time goes by, they'll improve in many ways that were never thought possible. ETH with its decentralized Blockchain, can achieve some purposes not viable on the EOS blockchain (which is semi-centralized). However, both are good cryptocurrencies that could take the world by storm if put up to their full potential.
As for me, I've invested into both ETH and EOS because of their promising technology. Not to mention, they have active development, and community support. Being among the top-10 cryptocurrencies in market cap, it shows that there's still interest from investors and traders into buying such cryptocurrencies. Despite this, no one can tell for certainty what will happen in the future with ETH or EOS.
Which means, that both ETH and EOS could either survive in the future, or only one of them will prevail.