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.
This is just one fact we all cannot dispute. The crypto market is so unpredictable and we cannot tell what the future really holds for any of them than to just be optimistic and hope for the best. Still, Ethereum has really had some real huge push this year even though some still feel it was over pumped, but the thing is nothing can be discarded for any market since at least for a while now, the support has somehow ben around $360 - $400.
BTC though, is really a coin that is of huge interest which is why it is always going to keep consistently doing better.