This is the knob shape that I have adopted for recent reel designs.
The profile is a concave curve. I like the appearance, and it provides a positive grip.
Last night I was talking to a prospective customer and the subject of knob material came up. He expressed a preference for a knob where the profile is a convex curve. The reason for this preference is that if the fly line became wound around the knob, it would not be able to slip off a concave knob (particularly so when the wrap overlaps itself; it becomes “locked”). I have created many strange tangles while fishing, but this one had not yet come up. It probably will now, since I know about it.
So I made the knob this morning. Had to make a new pan for the base of the knob, since my standard pan was too small.
Does anyone have other insights on knob shape?
North Branch Reels 
I think both knobs look fine. Like you, I would have the line wrapped around the concave knob just because of the comments cited. Perhaps that’s why the shape of the white knob is common and the concave one is something I don’t remember seeing. I like the caramel color of the concave knob.