BTW I like all the covers I've see on here so far.
Imrahi, I'd go with the speederbike back. Dynamically it's hard to decide.
As a group you have either:
Large face, facing left (ANH)
Far away faces, facing away (TESB)
Midway face, facing right (ROTJ speederbike)
The other option would be:
A villain (ANH)
Two main heroes (TESB)
Supporting characters (ROTJ C3P0)
Drew Struzan used the "Heroes", "Villains", and "Supporting Characters" theme on the Special Edition one-sheets. Nice!
Both back covers add to the green/forest theme of the front, so they're both excellent choices for ROTJ. These are honestly the best artistically crafted covers I've ever seen for Star Wars; Blu-ray or DVD.