its good to have a bit of both, never place your bets on only one horse!
I agree with you, it is better to have bitcoin and ethereum at the same time but you need to know do you have the money to buy both bitcoin and ethereum or not? and if your money is only enough to buy one of that coin, then I suggest to buy bitcoin only and do trade bitcoin pair usdt until you can have enough money to buy bitcoin and ethereum.
Having both ethereum and bitcoin at the same time and at your own account is so much highly appreciated. But of course you really must have your money to be use to but a cryptocurrency that is undoubtedly too much. Well it's up to you if you wanted have both or have one crypto for a time.