Gemstone guitar picks do not absorb vibration from the strings where as using your fingers absorb the vibration and does not allow the acoustic to resonate as long. For some people such as classical music players this is not only fine but preferred. For most other types of music the acoustic sounds great the more the top of the guitar resonates from the vibration being forced back into the guitar.
For electric guitar players it is a matter of preference. I play jazz and prefer the smaller picks to keep my fingers close o the strings. Come and visit the World's largest inventory and the largest selection, you'll be glad you did. Choose between all 4 popular shapes.