Even though I liked them all, I have to go with season 1 of Mighty Morphin Power Rangers.

Lost Galaxy is my favorite because this was one of the first seasons with no mentor the rangers had to rely on each other in a way no other combination had to before also this is the first season to have them working as professionals .and I tend to like that kind of season a little more then ones set in high school. They also had to deal with more stuff like Leo dealing with feelings that the red quasar saber didn't belong to him because Mike pulled it from the stone or Karone facing and starting to come to terms with her dark past or the team dealing with the loss of Kendrix. Plus they had the coolest zords in the Galaxy Megazord, Stratoforce, and Centaurus Unlike in other seasons where some rangers get lost in the background and don't feel useful every ranger had a skill that truly added something to the team.

RPM get in gear