Season 4 is pretty underrated in my opinion. I know that it consists of some ridiculous episodes (Beer Bad, just to name one) and Adam is...eh. But I really do love that season. I enjoy The Freshman, Living Conditions, This Year's Girl, Who Are You, and Restless is my favorite episode of the entire series. Most people rate season 4 as the worst, it seems. It's not my favorite season, but it might be one of them.
While I'm not a huge fan of season 1, it's not my least favorite by any means. I love The Pack, The Witch, Nightmares and Prophecy Girl... and The Puppet Show is actually pretty funny haha.