DVC as PP mention is designed to booked at 98% full every night of the year.
DVC very high season is mid-Sept through mid-Jan. (Most likely need to book before 7-month window to get desired availability.)
DVC high season is mid-Jan through mid-Sept except around the holidays when if goes back to very high season. (Much larger selection after the 7-month window.)
AKL-CL and value studios are the hardest to book IMHO.
GFV, BLT standard, followed by BWV standard are the next hardest.
BCV, VWL, GCV, & are next due to the small size of the resorts.