Me and a friend of mine have the 4 ball Rolling Thunder bag and they are great!  Easy to load and unload from the car because the bag separates easily, lots of pockets for everything, sturdy construction, several colors to choose from, and rolls nicely without tipping over.  
The only negative thing is that it is a little cumbersome because it is a bit wide, so getting down the aisles are sometimes difficult if the walkway is small.   Oh yeah, they also have a five year warranty.