I have round, sort of. On the right side of my thumb is ovaled a titch. The left side is round. I have a strange thumb, so I can not use pure round and didn't like the feel of real oval. It took me a few tries to find what feels good, works for me.
I would not suggest this to many, I use a workout tool to get the side the way I need it and if I screw up, it's drill out and do over ! The biggest reason, for me, I have a 'groove' so to speak, that is oval, if I don't get it just right, the thumb is to large and just doesn't feel right.
Probably not what you asked in the first place, but that's my 2 cents worth.
--------------------
AZ Guy aka: R & L Bowlers Pro
rlbowlerspro@cox.net
www.rlbowlerspro.comSleep is over rated.