KONA!!
the discs ARE a sweet feature to have, and they're pretty user-friendly. looking at the other two, i discounted the marin right away, as i'm not a fan of adjustable stems, but that's me.
the khs had no glaring shortcomings, but nothing to rave about, either.
the more you ride, the more you'll want to ride, and sooner or later, there's going to be times when you want to ride "for fun", and that's where the kona will show its pedigree.