Resource:s gather vs waiting on strategy

I’m trying to make a clash clone but I don’t know which kind of IAP should I use.

Waiting vs gathering?

Waiting is when you wait a certain time so it would fill up a storgae
gathering is when your units gather a small amount of resources or when you kill a certain enemy

when your resources are dried up, the only thing you could do is to buy more money through IAP but which one is more effective?

waiting a certain time or gathering resources through killing enemies?