Although I haven't actually seen season 2 in it's entire form I do believe that it is one of the best seasons of Buffy that there is. I have only seen up to the episode 'Suprise' and am really looking forward to watching Innocence as I know what happens.
The introduction of Spike and Dru was great. I actually love how sweet Spike is with her in the begining and I do love seeing him evil, it's great fun. In his first episode, School Hard, he was amazing and the first time you see him is epic. The guy really knows how to make an entrance. And although I don't like Drusilla much I do admitt that she added some slightly physco-like evil humour to the whole story. Overall, some of the best villians we've had on the show. Though I am a loyal Spuffy fan and all that, I do like myself an evil Spike.
Then, from what I know about the whole Angelus thing it seems pretty epic. I mean, I've seen him 'pretend' to be his bad self in season 3 to trick Faith so I know that it must be some show. It gives him some character, I say. It makes him more interesting to me, having him evil. I don't know. Maybe I'm just a sick person who loves seeing the guys all evil and killing people.
However, I don't have a favourite season, or I try not to. I also try not to have a least favourite. I think if I had to choose, from what I've seen, I like season 6 best but I do love season 2. Hah, heck. I love 'em all.