Good: S-25 Sled: Sometimes simplicity is best. The flat base and low profile design of the S-25 allows you to truly test you limits without worrying about tipping the sled.
Better: Rogue Dogsled: Used at the 2011 CrossFit Games. It can be used for both pushing and pulling movements. Sled drags and pushes are unmatched for developing a coordinated posterior chain. The Dog Sled is more portable than the Butcher, it will fit in the trunks of most cars.
Best: Rogue Butcher: The butcher adds more weight capacity and more grip options for increased variation.