I think you have to define "better."
If you want to ride several hours then racking is not the way to go. It's an energy intensive gait that puts great demands on the back as a racking horse must go hollow or it won't go at all.
The running walk, done correctly, is a very low intensity gait (maybe even lower than a trot). The back is level to slightly basculed, meaning the rear is fully engaged and taking some of the strain of the ride. It's not as fast, not is it meant to be. The flat walk is an endurance gait (that can be done for serveral hours). The running walk is a distance gait but not a speed gait.
So, define "better"!!!