Rangers commonly called overrated by the fandom.
The rangers that are most commonly labeled as "overrated" are Tommy, Jason, and Andros, which I tend to disagree with. Tommy and Jason are easy targets because of their popularity, while some fans on Power Ranger message boards have called Andros' leadership ability "overrated." Personally, I think these three have all earned their spots and popularity, thus imo, they're not overrated. I will say, however, that its unfortunate that Tommy does tend to overshadow an otherwise very good cast in Power Rangers Dino Thunder.
Rangers that I do see as overrated.
I'll start off with Kimberly. Kimberly is a pretty and lovely character, but to me she is overrated even by others who say she's overrated. Why? Well no offense Sean, but to start off Kimberly/Amy Jo Johnson is not hotter than every Sentai girl nor is she the hottest Power Ranger girl. Her fighting skills were rather, sub-par. All she could really do is kick and she was able to get by with her gymnastics skills. Her and Billy during season one were portrayed as the weak link on the team. Her actress, Amy Jo Johnson, however, is an excellent actress.
The other I would say is Billy. Billy was cool, and at times reminds me of myself growing up as a kid because I was always picked on, but to me he's somewhat overrated as well. The reason is because a lot of people choose him as their favorite blue ranger just because he's from MMPR, and often these fans choose ALL of the MMPR rangers as their favorites. While Billy matured dramatically by season 2 into a muscular, skilled fighter, he was the weak link along with Kimberly during season 1.
Rangers that I see as Underrated.
To me Cassie is the most underrated ranger of all-time. The reason is because she is overshadowed by other very popular pink rangers such as Kimberly and Jen. It also doesn't help that the cast of In Space tends to get overshadowed by Judd Lynn's story writing during this season.
Ashley is another In Space ranger that tends to get overshadowed by the series story writing. In particular I think her and Cassie get lost in all the drama between Andros and his sister Karone/Astronema, the search for Zordon, and the two part finale, Countdown to Destruction.
Ok while Kira and Trent are somewhat popular, I think both of them along with Ethan get overshadowed in this show by Tommy's presence. I actually felt that Doug Sloan did a good job developing the other characters around Tommy and didn't focus too much on Tommy, but Tommy is such a big ticket that his mere presence overshadowed the rest of the cast on Dino Thunder.
I think the cast of SPD is highly underrated, in particular Jack and Z. The cast and the series as a whole tends to get lost in the fact that it was both a Disney series and a Bruce Kalish written series. This series is actually ok, better than MMPR S3, Turbo, Lightspeed Rescue, Wild Force, Ninja Storm, and the other three Bruce Kalish seasons imo.