NTAXS and BMW usually run on Saturdays. SCCA and Equipe Rapide usually run on Sundays. (if you have a preference)
NTAXS is the only club with a cap on registrations (65). Recently, events are full before the first week is up - sometimes in the first few days registration is open.
There is usually no cap on registrations with the other clubs.
As always, the Autocross Calendar link at the top of the page has the latest event info.