Back between May of 2010 through to November of 2010 I smoked JWH-018 daily. It got to the point where my girl friend and I were going through a gram between the two of us a day. We would hand roll cigarettes and lace the powder in them that is why the use got out of hand we smoked them anywhere and everywhere. I am glad that stopped who knows what kind of damage we were doing to ourselves.
Of the ones I've tried, probably JWH-018 but I really like 5-F-AKB48 too. JWH-073 was about as good as JWH-018 but less potent and somewhat less intense.
I like Acetyl THCV... 1000x more potent than THC! Activity starts around 250mcg. Plus it is very chemically related to THC, so it should be just as safe as plain THC and many times safer than non-THC-family cannabinoids or the incredibly-addictive marihuana plant.