In my experience:
Chris King SS Hub, expensive but lovely, make sure you service them once a year and don’t expect the alloy sprocket supplied to last more than a couple of months in gritty or sandy going.
Hope SS Hub, good but the weak point is the freehub to hub body seal which can let mud into the pawl cavity and the six speed compatible freehub doesn’t really give you the ‘proper singlespeed’ look.
DMR SS with screw on freewheel, does the job for not a lot of money. Easy maintenance and looks good (in red) but be wary of spoke rub on your disc caliper with 29er builds.
Superstar SS Hub, not up to sandy soil, freehub is easily overwhelmed.
Halo SS Hub, unknown but looks good in the brochures.
Freewheels:
Shimano, Halo Clickster and White Industries are narrow enough to let you run 8 or 9 speed chains, cheapies restrict you to BMX chains.
I’ve killed a Shimano FW in the sticky mud at the Brighton Big Dog but otherwise they have been fine for me in my more regular sandy, muddy rides, as has my Halo Clickster which gives quicker pick up.