Hey Fred. I confess. I still don't have a bowl gouge. I initially ordered one from Woodcraft with a bunch of other stuff. When I opened the box, I realized that I had accidentally ordered a spindle gouge.
So, I did what any other tool oriented man would do. I kept it and ordered the right one.
(can't have too many gouges, right!?) Even though when I ordered the bowl gouge, it said they were in stock, I got backordered. So I waited. Then the backorder date got pushed back.
So I cancelled it and ordered one from Rockler.
I ordered a 3/8" with a fingernail grind. I can tell you from my limited experience that the fingernail grind seems to catch less (presumably because those pesky corners aren't there), but they are a pita to sharpen. I'm getting the hang of it, but it sure gets frustrating when you end up with a point on the middle.
I think 3/8" is a good "middle of the road" gouge to start with. The 1/2" will be too small to get at places like the corner at the bottom of a smaller bowl. I guess an advantage to a 1/2" would be taking out more material at once, but I'm still trying to learn how to be careful and cut slowly.