I've got packers for the rear, and rollers for the front, and I gotta say both designs have pros & cons. The rollers are much quicker to get in and out of, but the packers are a bit more versatile. Another issue worth considering is the material - some have a PVC coating on the outside (the shiny models!), and some have PVC on the inside (mine). I bought the models with PVC on the inside, and if your bags are tightly packed that can be a bit inconvenient - plastic bags, bottles etc all seem to stick to the surface.
I also bought the large handlebar bag, which still seemed too small to be very useful, but mounted so far forward of the bars that it affected steering a bit. AND the inside surface is stiffened plastic, and made for a noisy ride. In the end I decided not to take it on the tour, opting for a Lowe Alpine 'Mesa-runner' bumbag (fannypack?) instead. I'd recommend that option.