The effect of forward and backward sled pulling is a means to improve sprint performance, jumping height and overall muscular leg stiffness regardless of direction chosen. It has not been determined which method is more conclusive and gives better results. Both choices of pushing and pulling are beneficial.
The best suggestion - during some workouts the emphasis should be on pushing and some workouts pulling, and other training sessions the movements of pushing and pulling combined. However one chooses to construct workouts the weighted sled is a great way to improve speed and Get Strong.
The Rogers Athletic Drive Sled a Speed Enhancer