A tiller & disk do more or less the same thing. A disk is a LOT faster, but some of that is negated by the need to do multiple passes. A light tiller will dig a bit better than a light disk in hard ground.
Unless you are going to be tilling over 5-10 acres regularly, I'd go with the tiller. Its more maneuverable & flexible. A disk needs room to maneuver & a full head of steam built to properly fling & mix dirt. Everybody can use a tiller on a garden, most can't use a disk.
I don't see a scenario that a tiller would work in that a Harley rake would when trying to smooth stuff unless those are really deep ruts. In that scenario pick up a cheap subsoiler to rip things up then let the tiller or Harley do its thing. A Harley rake is designed to smooth/level & clean/filter dirt. A tiller will do both, but not as well as a Harley.