BNB is better to buy than ETH for now, given that Binance has a much stronger foundation in networking and has always been number one in the competition for exchanges. Even though it is based on the Ethereum network, BNB has more uses that are needed by traders, unlike ETH which is very widely used by scammers. I know this is not Ethtereum's fault, but at least there must be a solution to the many crimes that exist through the Ethereum network.
In order to understand which of the coins is better and more popular, just look at the use of the coin. BNB is used most often on native exchanges. It has almost no other use except for trading and investing. Ethereum is used everywhere. I do not know of any exchange where Ethereum is not traded. Most of the new projects appear on the Ethereum network, which indicates its popularity and demand.
Therefore, I choose Ethereum from two coins.