Hi Dick and all.
I used to have a bowl backed mandolin which is different from the A and F body styles referenced by Wesley S. It had an oval sound hole. Unfortunately the top caved in and it is not in a playable condition.
My other mandolin is an older Kentucky that has a spruce top and mahagony sides. Frankly I always liked the tone from the Kentucky Mandolin because it was brighter than the old bowl back. The bowl back was a good practice instrument but it always seemed to be much less responsive.
I like to use a pick that has a little more flex in it when I'm playing the mandolin--the choice of pick can make a difference on the tone that you get out of the instrument. Also, in this era of cutting corners, there are a lot of instruments out there that have plywood tops. IMHO There's no way that the plywood topped mandolin is going to produce the quality of tone that a solid topped on will.
I've taken the KY mandolin on some retreats and workshops to help provide some relief and I've had some of my colleagues remark that they thought that my mandolin (they called it my little guitar) had a sweet sound.
Dick, if you drop up for a visit, you are welcome to try out the KY mandolin.
I don't know so much about the way in which the quality of sound differs between the oval or f holes on the instrument. I did discover with the KY mandolin that the tone improved by removing the pick guard. I play the mandolin by holding my little finger against the top and picking which prevents the mandolin top from getting all scratched up.
My approach to selecting an instrument has been to go to a music store and to try a variety of mandolins or violins and then try to narrow down the selection by the way they sound to me.
Well, thanks for bringing up the topic. Cheers to all.