if you're planning to troop with it for 501st...a plastic helmet beats out a fiberglass helmet in terms of durability. My ABS Snowtrooper helmet(s) have dropped and simply bounced...
I've read several of these related threads though I'm an outsider to Star Wars collecting and trooping, and reading between the lines there appear to be three different attitudes about helmets, so that no helmet will satisfy everybody:
1) the collectors who want a helmet exactly like the original prop, often thin/cheap plastic, often crudely made and painted, etc.
2) the collectors who want a helmet that looks like an original prop when displayed but has a weight and solidity and heft when handled, suggesting to them higher quality.
3) the people who will be wearing the helmets as costume pieces, who have practical considerations such as weight, comfort, durability, ease of repair etc.
Seems to me there can be quite a gulf between #1 and #3: on the set there are people standing around between takes to adjust the costumes, and the costume only has to stay in place for a few seconds, the duration of an individual shot.
When the Stormtroopers marched in the Rose Parade their costumes had to stay in place for a
5.5 mile march.