Never did like the previous generation shimano road levers (current Sora). The current generation GRX however is pretty fantastic. It's markedly longer so my hands fit on them much better. They're also flatter.
I used to ride Sram S500 and then went with the current Sram mechanic shape, which I found to be an improvement. But after getting used to GRX I doubt I'll go back to Sram.
As to flat bar levers, doesn't really matter which I use. As long as the lever is 1 or 2 finger shape and has reach adjust it's all the same really. Grips are far more important in that regard.