BTC and ETH are an excellent choice. they are the most reliable and promising coins. However, I think that they will not give such growth as some altcoins. In any case, you need to have them in your portfolio, but I would also add a few promising coins from the top 10 -20, I think they will bring more profit in the future.
I would like to say that choosing from top 10 is better than top 20. Every top 50 altcoin looks promising but i will recommend to work with few project which are leading right now. There is no doubt that BTC and ETH is greatest coin of crypto industry doesn't matter you want to hold them or staking them. Beside that i love to recommend XLM and ADA. In my experience those coin have too much possibility to give you good annual profit.