[David66]

Personally, I don't see any advantage to going with a crab or omniwheel design. Unless you have a design from year's past or an excellent design and packaging team you are costing yourself valuable time. Not only will a crab system cost you weight and torque but if you lose one wheel, then you lose your entire system. Personally I would use a tank style drive system, and plain old fasioned wheels.
Strategically, a crab system will allow for some nice manouverability on the top of the hill. However, this could be countered by a single wing with suction cups. Also, unless its well designed, your crab system WILL NOT allow you to move instantly in any direction...it takes time fo rthose wheels to change directions.