Out of the two, I prefer ETH, and think it should have much higher potential. But, the market, on the other hand, is clearly still favoring BTC over others. Ten years is a very long time for this one, and impossible to predict, to begin with none of these has been around that long. This moves very quickly.
To be honest, I want to say clearly that predicting the future of a cryptocurrency is very difficult. Whatever may happen in the future and we may face things that are expected in the future. If you ask about certainty in 10 years, I choose Bitcoin instead of Ethereum. But if you ask about the next 2 or 3 years, they're both very good. You'd better invest in Bitcoin and Ethereum if you can. That's because Ethereum can be the second solution and backup plan after Bitcoin. If Bitcoin is having problems or constraints, we still have Ethereum. But for the near future, Bitcoin will have no problem.