You can always do both of them you can invest on both of them if you cannot decide. Bitcoins we all know that they are the king of cryptocurrency but they are too expensive to buy, and if you cannot afford that kind of value, probably go inveat to ethereum because their value is mot that expensive but have the same potential as the bitcoins. But it is just for me, it is up to you if you wanted to be believe me or not. For me ethereum will also rise just what bitcoins have done before. They are the king of the altcoins.