Ive found the 4 wheel works well on most carpets (DEN, PDX come to mind off hand) and moves with ease...on denser carpets at places like hotels (or streets with cobbles/etc) its a little more difficult and I tend to pull it from behind me on two wheels. I really think the 4 wheel is the best of both since you can move it either way based on the terrain. I would also say the Away wheels are decently better than my old Samsonite I came from or many of the cheap 4wheel luggage options out there.
When I am moving fast to make a connection I usually use the 4 wheels and not 2 behind me...I think its a bit easier to maneuver around slow walkers and such that way.