Both of them can be best based on your preference.

Ethereum transaction fee is not that high anymore and it's one of the most preferred coins of many that have been investing in Defi projects because it's needed for the gas.

But BNB, it's also noticeable that it had gained a lot of projects that are built on its network so it has a share too. Well, whether you choose BNB or ETH as long as you invest only what you afford to lose.

I think that's what all you need to think of.