I'm a fan of SP as long as the story is good (which should go without saying!). Bioshock is my number 1 favourite game of all time and will remain there for the foreseeable future simply because of the story (graphics & narration helped to). The Halo Trilogy and COD MW series also have great SP story that make them enjoyable. That being said the Borderlands Co-Op is straight up the best experience I have had in a game playing with other people and I also enjoyed the two L4D games. I should do more Co-Op to get a better feel for it but I would say I prefer Co-Op over MP, but usually play MP as that is what the masses play.