i don't know which one is my favorite or least favorite cause i don't own the series on dvd yet. & i haven't watched the show in years.
but i love season 1. at the time season 2 was totally different show. at the time it aired mind you. though i do remember reading an article during some season maybe the finale? where "Danielle Fisher" said that during vacation from season 1 she developed that fast. & it surprised the hell out of everyone. so they apparently added that in for season 2. the 1st episode. & it's a funny bit too. it took me a long time to like the high school years. cause the season i've seen the most is prolly season 1. and that season is the most different. that doesn't mean that's a bad thing.
you can only write certain material for 6th graders. a bit more after that season. & as they got older the show i think got better. though why they made eric have somewhat of a brain in the 1st season than later make him dumb as a post is beyond me. the sad thing is we really don't see much of these actors anymore. at least that i know of.