Mondays signify the first night of the scheduled magicians' one-week runs. The mansion is usually uncrowded, which is fantastic for seeing all the showrooms, the piano bar with Irma the invisible ghost, the parlours, hidden hallways and magic acts. However, some magicians are a bit nervous that night and still finding their stride, especially if they're from another country or have never worked the Castle before.
Wednesdays are Magician Member nights (special deals on restaurant fare for magicians), which means the Castle will be filled with more magicians per square foot than most other nights. If you've ever wanted to see a bunch of magicians scrutinize a bunch of other magicians, Wednesdays are the perfect opportunity. Also you'll get some bonus magic from impromptu shows pretty much wherever you are. Fun!!
Thursdays are great because the place is a bit more crowded but not as crowded as Friday or Saturday. You'll be able to see any show you want, usually with supportive audiences.