Info:
There have been 4 ever-improved versions of the Nexus 8: the SG-8R*20, -8R22, -8R30 and -8R31. The improvements have to do with hub sealing, shift quality and some bearing upgrades.
There have been 4 ever-improved versions of the Nexus 8 Premium (a.k.a. "Red Band"): the SG-8R25, -8R27, -8R35 and -8R36. The Premium includes some needle bearings where the regular Nexus 8 has plain bearings.
The -8R35 has two roller clutches instead of ratchets. The latest (
AFAIK) version, the -8R36, has three roller clutches and is silent in operation. Shifting is fast and buttery, and reports are the hub stands up to off road use and is well sealed.
The Alfine versions (SG-S500 double roller, SG-S501 triple roller) adds some cosmetics and the ability to fit brake discs.
Opinion:
Get the SG-8R36!
HTH,
tcs
*"R" for freewheel hubs that can fit optional roller brakes; "C" for coaster brake versions.