I think that if it is a long-term investment then you can buy both, Bitcoin and Ethereum are all very potential altcoin and will bring us profit in the future. You should invest heavily in bitcoin if you want to make a big profit, because bitcoin is the king of the altcoin and it always has the high pump, but the price of bitcoin is very high and there are always risks. Unlike bitcoin, ethereum is cheap, and stable, it has many advantages over bitcoin like low transaction costs, faster transaction speeds.