[Al Skierkiewicz]

Mk,
Casters are perfectly acceptable but have drawbacks. When moving from a forward to reverse direction the cater must rotate about it's vertical axis which requires some side to side motion to accomplish. If the robot is in a position that it cannot move sideways, the casters will actually fight your commands. Other robots can direct your robot actions by pushing on the side of the robot where the casters are located. Omni wheels react the same way.
On tilted surfaces, they have a mind of their own. While they may work this year, in a year where climbing, ramps, or bumps are part of the game, casters are by far from the best choice.