In the Super Sentai fandom, fans of course always argue which seasons are the best and which are the worst. Now, during the Saban/Lynn Era, many of the fans are very split on which were the best and which were the worst. Being the era of following Sentai's ways, while having great quality, it was inevitable that the fans are so divided in this era.
Power Rangers in Space. Many fans absolutely loved the story of Andros and Astronema. And fans also loved the search for Zordon and the space themes that supported it. And "Countdown to Destruction" is considered by many to be the best finale ever, wrapping up the six season long story. The characters also got a lot of good character development.
Power Rangers Lost Galaxy. Lots of fans were torn on this season. A lot of this has to do with the transition of the Zordon Era to the Saban/Lynn Era. To all fans, it also depended on if the story made sense to you or not. Some fans thought Lost Galaxy's story was perfect. And other fans thought Lost Galaxy's story was mostly incoherent and lackluster.
Power Rangers Lightspeed Rescue. Considered by many to be the worst of this era (unless you count Wild Force). Fans really disliked the episodic nature of this show compared to Lost Galaxy and Time Force which had more arcs going on for them. Fans also criticized Lightspeed Rescue for having a lame motif (rescuing), "bland characters," and terrible team-ups. Though fans of this season view Lightspeed Rescue as having everything you'd want in Power Rangers. Though strangely, they seem to be few and far in between. Hey DancingAlienDude. I know you absolutely love Lightspeed Rescue. Perhaps you'd like to add on to this?
Power Rangers Time Force. Another very popular season. And considered by many to be the most well made season out of them all. Time Force fans are often in conflict against the In Space fans. Space fans often criticize Time Force for copying too much from Timeranger, calling it a lazy carbon copy. Time Force was praised by many fans for easily being the darkest story in the era, allowing elements like death, intense drama, and terrorism. And fans considered Time Force to have some of the best acting ever in the franchise! And the cast was very well liked by fans.
Power Rangers Wild Force. For those who count Wild Force as part of the era, it is considered by many to be the worst season in the era. Due to being an even more carbon copy of it's Sentai counterpart than Time Force, having below par acting, and the overuse of zords. Fans also accuse Wild Force for setting up the style that would evolve into the style used for the Disney seasons. Fans greatly praise the two team-ups that are present in this season, but rarely anything else in it. Considered by many to be the best team ups in the show to date.
So overall, it seems like In Space and Time Force are the most praised, due to having a strong coherent storyline and likable characters. While other elements like acting, borrowing sentai material, and overall performances kept the fans of these two seasons against each other. The whole Zordon Era vs Saban/Lynn Era also plays a role here. Lost Galaxy was hit or miss by fans. And because of that, it has a hard time keeping up with Space and Time Force. When fans love Lost Galaxy, to them, it can easily beat both Space and Time Force. But when they don't, fans rank Lost Galaxy below those two. Lightspeed Rescue gets even more criticism for it's episodic format and for just being plain "lame" with it's motif. As a result, Rescue often has difficulty keeping up with Space, Lost Galaxy, and Time Force. Finally, Wild Force mostly seems to only get praise by fans who loved seeing Gaoranger in English. Usually, it doesn't really compete much with the other four seasons.