I love a well put together Mecanum system, but the fact of the matter is that nothing on this list can touch a simple, elegant 6WD (8WD this year) with a drop center. Just ask 1114, I haven't seen them deviate from this strategy for a great many years.
A crab can match it if done properly, but I bet a poorly rookie team could build a solid 6WD much more easily (in fact I know they can, just look at 2056's rookie robot
http://www.chiefdelphi.com/media/photos/28599).
But if it is purely omnidirectional motion you are looking for, Mechanum is pure holonomic, and easy to build/maintain.