I think I've done ok here, but I'm sure someone will chime in if not
(I've been wrong before.. once or twice :lol )
1. eFx Legend; ANH, derived from Rick Baker molds, with some cleanup deemed necessary for licensed mass-production. More accurate paintwork than the Limited, but looks more "factory-made" than something like the Muir, Quasi, JB, or other fan-mades.
2. eFx Regular; ANH, derived from same molds as Legend, with (despite what was advertised) I believe the same cleanup as the Legend. Less accurate paintwork, looks evenly sprayed versus Legend's brush strokes of the gunmetal. Same dome on each helmet.
3. ANOVOS; ESBwith some ROTJ Reveal features, more "inspired by" than directly derived from any one source, kind of a blend of influences. Inaccurate in some ways that I'm unclear on, probably good option for wearing (though still heavy fiberglass) but less so if accuracy to any one movie is desired.
4. Brian Muir; ROTJ based, "fan-sculpt" (only insofar as being sculpted by Mr. Muir after the fact, based on his recollection/idea of Vader (I believe?) Some "inaccuracies" to ROTJ but does not claim to be an exact ROTJ replica, so a good option for someone wanting a helmet crafted by the by the very same hands that crafted the originals.
5. Quasimodo; 3 flavors: ANH, ESB, ROTJ, fan-sculpt based on a flawed Ghost Host casting, but significantly different in appearance. Stated intention of sculptor/painter is to capture the "essence" or "soul" (my words) of Vader, versus the "provenance above all" idea (which one could argue describes the EFX lids). Less technically accurate in shape perhaps but has the "look" of the real thing. Comparison of the battered-looking ANH Quasi vs. the somewhat toned down paintwork and finishing of the EFX Legend shows this.
6. JB ESB; ESB, fan-sculpt I believe, to be honest I don't know much about this one and so I'll leave it to others.
7. Sideshow; Bust versus just a helmet, original is ROTJ Reveal type but with a distinctly different "look" with the dome on. Follows in the tradition of Sideshow taking some "artistic license" as far as accuracy is concerned. New version bust without removable helmet is a bit of an unknown to me.