Experience in this group thaught me:
Any fan-made helmet around is the biggest (and probably the most accurate) helmets around. Now, comparing each other side by side...that's another story.
Any licensed helmet (i.e. Rubies, Don Post), are NOT ACCURATE in size, and mostly made with kids or young teenagers in mind (too small). From the whole crowd: DP' 95 (specially the one with WHITE INTERIOR -which is rare- is the biggest, and probably the best option if you go that way. I had one of those.
DP made also the DP 96-97 (the latest one, being the worst of them), but better than Rubies. The licensed helmets were reducing, both in size and quality as the years progressed, changing the license to Rubies in 1997 or 1998 i believe, who ended up with the DP molds and then messing the product completely.....aka. making CRAP! Flimsy, narrow, smaller, and definitely NOT ACCURATE in any way, but making the product even awfully-looking.
uke
The Don Post Deluxe, which was in FIBERGLASS, while DEFINITELY BIGGER than the regular DP and Rubies counterparts, tried to recreate the look and feel of the real helmet....still, not accurate from the screen-used ones, and yet slightly smaller than the screen-used or Fan-made versions. My helmet as of today is a recast of the DP Deluxe I bought on Ebay couple of years ago. Only difference you could notice about the DP Deluxe is the markings, dings and scratches that are actually indented into the helmet...that you could literally feel them with your fingers...making it realistic, but not perfect.
Now, couple of artisans around here (FP, MS, GF, Sarge's, etc.) made awesome versions, more accurate, dead-on with the size and shape, but they all have also few differences between each other....all depends on what you're looking for. There is a thread around (not sure if it was deleted or not....MODS???), that mentions the difference in helmets according to the movie (i.e. ESB and ROTJ) versions of the helmets are different from each other, and not necessary about the colors or paint scheme, but in shape and size. It was something like FP's MSH (1 and 2) and Natty's helmet comparisons, that the first one was perfect for ESB, and Natty's for ROTJ.
The option is yours, of which version suits you best.
Robert
