To tell the truth, I use both services. Coinmarketcap is longer on the market, but I have the impression that the process of listing new projects is much longer (I think at some point they made a business out of charging a lot to speed up the listing process). Coingecko, in my opinion, is listing small projects much faster. If someone likes to invest in new, little-known projects, Coingecko will be more practical for him.