I recently received feedback on a layout for a 4-layer board (which contains several switching power supplies) that has me questioning some of the practices I have been following regarding the routing of signals. I was originally taught to keep as much of a given signal trace on the top copper layer as I could, and to only dip down onto the signal layer when necessary. While this resulted in the ground plane being fairly broken up on the top copper layer, my sense was that as long as I had vias that connected to the internal ground plane in locations that would help reduce ground loop area, that this wasn't really a problem. I also additionally add a ground fill to the signal layer, so there is a fair amount of ground plane on this particular board. The feedback I received, however, indicated that it would be much better to maintain an unbroken ground plane as much as possible, (on boards with switching power supplies particularly), and if I needed to route most of my signals on the internal signal layer, then that was fine. I'm wondering what approach people here prefer.