Theoretically speaking, the "Solid Axle with External Preload Collar" is the most optimized. That being said, it still comes down to execution. Bearing sizes, material use, and manufacturing tolerances all play a role. Both the new Shimano XTR and Chris King front hubs feature this layout. The large-format King bearings provide better performance. I'd like to add that this is no fault of the hub manufacturers. All of the various configurations work excellent with conventional forks. There hasn't been a real need to look at front hubs differently until this point.