I don't have any experience other than my current rack and bag, which is a Topeak Explorer rack + Topeak MTX EXP bag (with expandable panniers). I like it, I can carry my laptop comfortably in one pannier, clothes in the other and lunch and toolkit, puncture kit, phone charger in the main compartment.

One issue I saw was when I wasn't using the panniers - the bag can rattle a bit in the rack. Not too many people seem to have reported it, and I solved it by simply inserting a piece of folded paper between the rack and bag when sliding the bag in. Since I don't often use the bag without the panniers, this doesn't bother me much. The panniers tie down to the rack - that probably helps the bag to not rattle in the rack.