For trading, I prefer to choose BNB because it is clear now that the average BNB holder gives them a lot of profit, and when compared to investing, I would suggest using both of these coins, either BNB or Ethereum, because both are very good coins.
If it can be great for both in terms of investment, why don't you suggest both to trade too? because Ethereum is also not bad to trade as long as the market can be very supportive and Ethereum also often experiences price increases along with BNB and also with BTC. So it won't be bad for both in terms of trading and also in terms of investment.