From Team 449 Wiki
Mecanum wheels allow the robot to move in any direction. Each wheel is powered with a different motor, and by changing the direction the wheels spin allow the robot to change directions.
There are small disks around the circumference of the wheel, allowing the wheel to be driven forward with force, but also slide left or right easily. The is optimal when the goal is to have the robot turn smoothly. The robot can move easily in three directions (holonomic drive frame).
Colson wheels are likely the most common type of wheel used at robotics competitions. The Colson wheel is ideal for many needs because of its durability and traction.
Similar to a tire, an outer rubber wheel surrounds a rim. Air is forced inside of the wheel to create pressure. The advantages of a pneumatic wheel is that it provides shock absorption over uneven and bumpy surfaces.