I think both of them will be successful in the future, but if you tell me to choose one then I prefer Ethereum, because Ethereum is used by many projects, so Ethereum will definitely be successful until there are no more projects that use the platform from Ethereum, but in my opinion it's impossible because now there are more than 100 projects that use the platform from Ethereum, so that Ethereum will definitely be successful in the future, while BNB is an exchange project, so if there is another exchange project which is better and more popular than BNB, then I think BNB will not be popular anymore (although other exchange will find it difficult to beat or replace the popularity of Binance, because everyone is comfortable trading on Binance).
They are both good, profitable and reputable coins, end of the discussion. No doubt about it! I guess our answers just varies base on our preference. Me? I prefer eth before coz we know that it was Rank 2 and that single thing speaks a lot already. However, I realized that BNB got a greater potential. Binance is a dominating exchange up to date and its legacy continues so I disagree to you that Binance will no longer become popular. I mean more and more investors are trusting their services thus a greater chance for them to trust their own token as well. The more investors means greater price as well. Unlike eth, its image someimes get into trouble.