CLV - Constant Linear Velocity
The disc is written at a constant speed and maximum performance.
CAV - Constant Angular Velocity
With this, the disc is written at a constant marginally increasing speed until it reaches it's maximum speed with coincides with the end of the disc.
P-CAV - Partial-Constant Angular Velocity
The disc is written to at an increasing speed until it reaches it's maximum and from then on the transfer rate remains constant. P-CAV drives are faster because they reach their maximum speed much earlier.
Z-CLV - Zone-Costant Linear Velocity
Z-CLV is only used in the writing process and the way it works is that the drive is divided into a series of zones. After each zone, the write speed is increased until the last zone is burned at maximum speed.
Really, each method has it's advantages.