Both are useful tools but CMC is more popular than Coingecko! Coingecko has something unique features like Exchange trust score, ICO review and many more but CMC only has token price chart, trading view and exchange rankings which also have in Coingecko! But CMC has some strong rules to get listed there where any coin/token project easily can get listed in Coingecko, that's why it has more coins listed than CMC! To me, this lot of token listing is a drawback in Coingecko!