I personally would prefer Ethereum, because :
1. Ethereum is more experienced than BNB
2. more people trust to invest in Ethereum than BNB
3. Ethereum price increase is higher than BNB
4. more projects use Ethereum than BNB
5. Ethereum ranks 2nd on coinmarketcap while BNB ranks 4th on coinmarketcap
6. many people agree that Ethereum is the king of Altcoin
that's my reason why I prefer Ethereum rather than BNB at this time.
what if bnb followed in ethereum's footsteps. do you still choose ethereum?. if you look at the development of bnb the same as ethereum, so it could be in the future bnb will replace ethereum.
I personally choose both, because they are the best. these two coins are good investments, so I choose both.