which is more difficult rolling harrier or a one roll circle ?

You are comparing two very different disciplines. Generally 3D is flown for fun, and to impress. Its the sort of flying you often see at the shows - low level daring stuff. Its intentionally flown to be entertaining to watch.

Smooth precision aerobatics is entirely different and is judged in a completely different way to 3D.

Apply the same judging criteria to someone doing a rolling harrier and someone doing a 1 roll circle - ie you are looking for perfect symetry, constant roll rate, etc etc etc. The you will find the two manoeuvers are as difficult as each other to do to the same standard.

However its pointless judging 3D like that - 3D is for fun and a way of relaxing when you have had enough of your IMAC practice but still want to fly.

Variety in your flying is the key to making yourself a better pilot.