I used to think the bowls were the better deal. They do give you a little more ear/driver distance, which helps "open up" the sound. On the other hand, they also give you less bass. The problem is that there are three layers to these pads. The bottom layer is thicker, because it has to maintain enough of a shape to hold the pad to the front grill. The top layer is also thicker, which makes for a better contact surface. In-between, however, is a soft layer. This keeps things airy but in doing so, it leaks bass.
The flats fix this problem by providing less ear/driver distance and a thicker top layer, with much less leakage in the bass. They're problem is that they can end up muffling the sound. You need some ear/driver distance.
Some time back, I tried various experiments with the bowls. In one, I cut out the middle layer. In another, I stacked the bowl pieces, without the middle layers, to produce homemade cushions that opened-up the soundstage without giving away the bass. I liked the result better than the use of the jumbos.