During pre-production, things change. Some designs may change or vary. Also with logos, sometimes the higher ups don't like it and finalize them. Sometimes they are just place holders for something better. It is unknown why some of these changes happened. There are also some logos slightly different with Wild Force, Dino Charge and Megaforce but they are minor edits so I didn't include them.
Mighty Morphin Power Rangers (1993-1995, 2010)
Mighty Morphin Power Rangers logo (top left) logo is the show logo. The toy and merchandise logo (top right) and the international one omitted 'Mighty Morphin' (bottom left). The 2010 "reversioned" logo for the Disney re-edited episodes.
Power Ranger Zeo
Power Rangers Zeo originally was going to be called "Zeorangers." The logo was going to be originally used on the show and used in early promotional items that public was not meant to see. The logo was also used internationally on toys and merchandise.
Turbo: A Power Rangers Movie
It originally was going to be called "Power Rangers: Race to the Volcano," here is an early promotional from Jackie Marchand with said logo.
Power Rangers Turbo
This "Turborangers" logo was used on international toys.
Power Rangers Ninja Storm
Same logo, just different coloring. The right logo was seen on an early promotional flyer. I like the final one (left) that has the colors of the main trio: red, yellow and light blue.
Power Rangers SPD
The original logo to right had very little color and alternate style font. I like the finalized one to the left.
Power Rangers Mystic Force
The alternate logo to the right was used on some merchandise. I like the left finalized logo with the design in back.
Power Rangers Jungle Fury
Similar logo but different colors and the F and Y are bigger and Jungle is in white and smaller and different font.
Power Rangers (2017)
The 2017 movie logo is silver with red highlights with bolt in center in a straight line. One of the prototypes was red and blue background with two lines and thunderbolt R and P.