I liked Season 2 the best. 3 was awesome, and I love those episodes, but it's shorter and a little too reliant on running jokes. In no way do I think it is worse because of the Rita storyline. I loved that one. It's just a tiny bit worse than 2, and 1 was amazing, but some of the characters, Buster and Gobias (as in Go Buy Us) particularly, didn't seem to come into their own for a while. It seemed like they were one character one minute and a bit different the next.
But still, all were amazing. I loved 2 the most due in part to all the changes. George Sr. in the attic, and all the hilarity that insued there. ICE, Yam-egg-plain-her?-Ann, Buster's hand near the end. I don't know. It just seemed like it was the most fun to watch.