Samurai/Super Samurai- Or as I like to call it, the 4kids dub of Shinkenger. They made the mistake of trying to Americanize a Sentai season with deep roots to Japan, resulting in a season that lazily copies/translates the beats of Shinkenger verbatim.
Megaforce/Super Megaforce - Easily the worst season of Power Rangers to day. It's poorly written, it's lazy in almost every aspect (characters, story, villains, use of Sentai footage, etc), and the Legendary Battle is very underwhelming. It tries to hard to recreate the feeling of MMPR, that it come off as a rip-off. Megaforce clearly wanted to modernize the formula, but only revealed how stale and dated it had become.
Dino Charge/Dino Super Charge - The best season of the Neo-Saban Era by far. It's far from perfect and the ending is a bit dodgy, but I think it's held together by the chemistry between the extremely likable cast of characters.
Ninja Steel/Super Ninja Steel - I'm a bit more lenient on this season since Nininger being such a terrible season gave it such little to work with. Ninja Steel at times feels like a parody of Power Rangers with how the characters are handled, the childish humor, and the lack of any kind of stakes or tension in the story. A pretty boring season all around.
Beast Morphers - It's not without its flaws, but Beast Morphers is far and away the best Power Rangers season since RPM or Dino Charge. It actually feels like the people involved with the show put genuine thought and effort into the story, the characters, and the action. Also, Steel is the MVP of this show.