Personally, i always prefer Speed Shampoo... Its just awesome due to its ability to clean and leaving slicky and smooth surface behind, and that too in an affordable manner. whereas, NXT and Ultimate wash & Wax do slightly the better job but u need to pay little extra along with fancy name and bottle 
Brother, many brothers discuss shampoo preferences. But, Besides the shampoo brand, It also depends on our geographical location as well because of water....
For example here in Karachi we mostly have the Hard water, and on the contrary u guys enjoy the soft water (even in lavatory
:P). Thus, the shampoo with soft water dissolves better and gives better bubbles, resulting in better cleaning ability and leaves slicky surface.
I personally, make shampoo solution in drinking water (sometimes, not always) for flawless results.(H)