I know all about the plans for reusing the 1st stage, ocean landing vs. fly back, etc. But, Musk wants to make stages 2 and 3 reusable as well. Surely they would have far too much velocity and height to turn around and come back? Or, would they just go for a long ballistic arc to somewhere in Africa on the 2nd, and circumnavigating the planet with the 3rd, to return to the launch site?
Elon Musk has said that they have basically given up on Falcon 9 upper stage recovery, focusing on first stage recovery for Falcon 9, and whatever you want to call Falcon Heavy's side boosters and center core. The center core is not quite a second stage, but is kind of sort of a second stage. Stage 1.5?
For the upper stages on a LEO mission, it is basically in orbit. On a GEO/GTO mission it is in a pretty high orbit.
Getting that back is basically the same problem as a Dragon recovery, which is probably going to add a major payload hit.
For upper stage recovery they have decided that BFR (Big F***ing Rocket) they plan for Mars missions, using the a cluster of Raptor (million lb thrust LOX/CH4 engine) will be reusable on first stage and second stage.
There has been some confusion and suggestions that in fact, the second stage of the BFR will be the MCT (Mars Colonial Transport). That is, the first stage delivers the second stage which proceeds to orbit. Possibly is refueled by other BFR launches, and finally departs for Mars.
In that case, many BFR/MCT launches will likely be needed to refuel the first MCT waiting to go to Mars. So upper stage reuse of the MCT will be critical.
So to the actual question, where would they land?
Well they will basically be in orbit once they are ready to land, so going once around and aiming for the launch site is likely possible, assuming their orbital inclination did not move them too far away from the launch site. If they have sufficient aerodynamic control they can likely make it back to the launch site.
Smartest place to land is wherever they intend to refurb them for reuse. Likely the launch site, but that is unclear.