If you have knowledge and insight about middle schools, share them here with other parents.
Remember, however, that a school which is great for you and your children might be a nightmare for someone else, and vice versa. So read and learn from others opinions, but definitely explore the schools and reach conclusions on your own. Take part in as many school tours as possible, and visit the Enrollment Services page on the SPS website for enrollment guides and other information.
The only middle schools I know anything about are alternative K-8's: Salmon Bay, TOPS, AS#1 and Pathfinder, and I've heard very good things about all of them. As Carla Santorno points out, if you choose a K-8 school, you can't expect to have as large a variety of course offerings as in a traditional middle school, but there are tradeoffs in terms of size and community connections that make it worth it for many parents and their children.