Both were good in quite different ways.
The Time Tunnel was like a science fiction version of You Are There, a show literally meant to bring history to life, with Walter Cronkite doing "modern" interviews with people involved on both/various sides of major historic events. (This ran 1953-1972; see https://m.imdb.com/title/tt0045458/)
While being at major points in history, the two colleagues lost in time in the Time Tunnel were often making sure that history worked out as they had learned it (thus, "preserving the timeline" in Star Trek terms; for a very different take, though, there is a discussion of time travel in Avengers: Endgame which is very good and differs).
OTOH, Quantum Leap seemed to be about more normal people, though it would shed light on important other people or events.
In both cases, the acts of ordinary people helped move things, though these actions were supposed to "keep history on track" for the Time Tunnel, while righting wrongs/helping people was a theme of Quantum Leap.
