Rocketman is the most plausible. The following three items list the rationale for this conclusion.
1) Lucy in the Sky references a fanciful experience detached from reality.
William Shatner is a level-headed captain.
2) Space oddity references hopelessness while drifting in space within a damaged spacecraft.
William Shatner typically seeks resolutions and would not surrender to helplessness.
3) Rocketman references a reality-based perspective of missing family, eventually returning home, and the dangers of mars.
William Shatner is best suited for this song as it befits his general demeanor and a Captions role.