This is a matter of some debate amongst those who are interested. Some are loathe to call the best proof and at one time called them specimen.
Few are frosted, though on the proofs the field and devices are not quite IMO of the same finish. The edges are squared and the device details crisper.
I once tried to describe this and point out examples: the cross on the orb itself (really more of an inverted "T" should be fully detailed and clear (NOT the cross that surmounts the orb), the flower stamens should all be clear and separate. On the obverse, the moustache, eyebrow corner, beard, and ear lobe all the way round should be crisp with excellent detail. There are other bits, but these are important and key areas. The denticles and edge milling should be sharp and defined. Simply a reflective field is just not good enough, and I think viewers (and graders sometimes) can be deceived. Actually hard to capture in but a few words.