They are both difficult in their own way. ROTJ is very random, and the damage in some cases doesn't even make any sense. There is also alot of misting between layers which makes it a bit tough to duplicate. ESB is more straight forward, but is VERY tedious in that there are alot more layers to contend with, specifically on the back panels.
FFo$ did a fantastic job on this, and i know Starchild will be thrilled with this helmet on his head lol