I like Digimon too.
Favorite = Season 4. 2nd Favorite = Season 3. I didn't like seasons 1 and 2. I haven't had a chance to watch the new season 5.
Watching Shakugan no Shana still. I have to say the 2nd season is much worse than the first. I don't like the new character. They already had one of her type (the shy girl) and didn't need another one. Another problem season 2 has is the lack of a main villain, at least in the first 7 episodes.
SnS spoilers follow...
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In season 1 episode 1, they introduce a main villain. They kill him off later, but they never failed to introduce a new main villain, either in the very next episode or 2 eps later. In the final ep of the first season, the main villain was defeated but not destroyed. They simply failed to reintroduce the main villain at the beggining of the season. They are currently stuck in a "good guys getting to know each other" arc which isn't very interesting to me. Also, there's not enough fight scenes. This is helped/caused by the lack of a main villain. The fight scenes that are there are "training" scenes which lack the intensity and emotion of real battle scenes.
Almost caught up... SnS Season 2 ep 14 recently aired in Japan. Currently on season 2 ep 7. I love this show way too much.