They are both the best in their own ways.
Bitcoin is the leading crypto and there's no doubt about it. it dictates almost all the prices of altcoins, and it increases yes day by day.
Ethereum on the other is also best, which a lot of altcoins is using its technology.

but if your looking for investment, this 2 could promise a decent return of investment.
but my advice is you look up to a lot of upcoming projects, where you can buy from its cheapest price and wait for the moon!