Btc and Eth both are leading coins in cryptos. These both coins have their own hold in the market. I would say dont invest all money in single coin. Invest your money partially in Btc and rest in eth. Both coins are suitable for long term holdings. To ensure stable and risk free returns invest in both coins.
You can add more coins in your portfolio if you think that you can still manage them well but if not, you better stick into 2-3 coins.