Welcome to TDH Dan! Choosing a helmet can be a real confusing task these days, but im going to try and help ya make an informed decision.
If you want the absolute best in accuracy id say go with a Fettpride FPH2 ROTJ. It is fiberglass, and has all the ROTJ physical damage on it and really is a beautiful helmet. Keep in mind though that FP is a very busy dude and he usually has a significant wait time.
Other than that, there is Animefan, which is cold cast from FP's older premium helmet molds, based off a modified prototype of the Master Replicas helmet...another great fiberglass helmet, that is not movie specific and you can get a great ROTJ version from it.
There is also Bobamker, who makes an excellent fiberglass helmet. He also has significant wait times, but puts out a quality product as well. He is located overseas though, if that matters to you.
I also cast fiberglass helmets, based off of the production Master replicas helmet and although i usually push my ESB version, i also have a non movie specific version that can be made into a nice ROTJ as well.
There is also ASOK who has FP's old GMH helmet molds (do a search here for the Grant McCune helmet for more info on that)...a slightly smaller helmet, and cast in cold cast urethane resin.
I believe Terminal Fettler sells helmets as well, but not sure if its a painted only deal or not, you'd have to contact him to verify that.
Fiberglass helmets are not only screen accurate in material, but they also hold up better to normal everyday abuse and can withstand a good amount of heat without warping, as well as beiging failry light weight, depending on the thickness of the casting. The only downside is they are usually slightly higher priced.
Resin helmets, although fairly durable, can warp when exposed to too much heat, like being stored in a closed hot car in the summer after a troop or something similar. They also can shatter when dropped, as a fiberglass helmet will either chip or crack, but not usually shatter. So with resin helmets you just need to be a little more cautious. Ive known folks to have resin helmets for years so its not like they are crap or anything lol
I hope this info will help ya out.... have fun and be sure to research anything your interested in buying before pulling the trigger!
I also sent you a PM with additional info.