Everyone has their own opinion
Everyone has their own opinion, but I like the mid 1940 gas port rifles, next to that would be the 1941 Winchesters
"Really rare"? Hmmmm, ....
There is some of the experimental stuff, like I got to see a legit experimental box magazine Winchester (flat mint and gorgeous). There is also an early experimental coating called 'pentrate', but there might only be one of those left though ...
It is hard to collect stuff like that, though. But then some of the experimental stuff is rare but a bit more available, like the teflon coated Garands? I got to see one for sale here at a very high end gunshow years ago (and of course they wanted a very high end price ...). Then when I got to go down to Quantico I saw a whole rack of about a dozen of these funny greenish looking Garands - sure enough; teflon coated. Very neat and they even feel a little slippery. USMC tested the coating somewhere in the 50's, IIRC. I don't know how many were ever made but some of them managed to find their way out into the world.
There are also the ones that you just don't really think of. I think it might have been Dick Culver who spoke of a rack of HRA M1D's (or was it Bob Seccombe) while he was in the service. I have seen plenty of SA's and WRA's and know of one IHC that was sent out of the CMP, but I have never seen a papered HRA. That would be a neat rack of rifles - all 4 makers in M1D's.