both of them are popular tho cmc is a little bit more popular than gecko but imo gecko is more accurate when it comes to coins data so many people are using it therfor  ,
 you can go with coingecko first  and then maybe consider listing in cmc later on  .
 listing on these top sites may add impression to your coins but your right that it can also depend on other factors  such as the usefulness or the purpose of the coin and so on ..