I've used both extensively. I find them to be both just about as effective. I prefer ECA stack because it is simple, you don't have to ramp up like you do with Clen, you can run it for longer and your body will still be reacting to it instead of getting used to it, and it is legal over the counter. I also combine T3 with ECA, I don't know why some people believe you can only stack T3 with Clen lol.