You can say any you want, but CoD4 onwards is better as more people have played them. My least favourite mission is Goalpost from MW3, very boring and predictable. Also a bitch on veteran. Close behind would be the entire American campaign from WaW (repetitive). My favourite mission is All Ghillied Up by quite a margin; its the only true stealth mission in CoD history and has the perfect setting (Chernobyl). I also like Black Cats from WaW, new and fresh.