My top 5 would be
1. Mighty Morphin
This season will always be classic and the template for success.
2. In space
Bringing the second cast of Power rangers turbo proved to be a great idea. That showed fans grew attacted to rangers outside of MM.
Androse was a complete bad ass and the plot remains one of the best of the series .
3.RPM
Here they dived into a more darker, apocalyptic world and it paided huge dividens. The season brought back a lot of OG fans and the Scott/Dilion friendship made it special.
4. Dino Thunder
If it weren't for DT we might not have had too many seasons after to be honest. This season is what got me back on track and introduced only a 5 ranger cell. With Tommy many times taking a step back to allow Carner to succeed and grow.
BTW Trent was a bad ass white ranger second best all time.
5.Zeo
Great to see the rangers get more powers and be transitioned to a new season. Tommy truly became the face of the franchise here and Jason coming back as the gold ranger was beyond epic.