It's kind of personal preference. I use a 1" shallow one, and a 5/8" half round, as well as a curved spokeshave. I have both inny, and outies. I've seen Ian P Ratt use a half round molding plane, under the cheek while demonstrating at Dixon's, and someone else use a bowl skorp. (I think that's how it's spelt) It's like a curved draw knife.
Bill