I've a couple of thoughts. Don Derry, who sells a gated hollowing
system, says that the "art" is on the outside of the piece. Hollowing
only gets the sawdust out of the way. Therefore, whatever tool you
use, make the hollowing as easy and painless as possible.

As for solid shapes, I like solids that fell good. Spheres feel good.
Eggs feel good. A few others feel good too.

The only call for hollowing is that an item might feel better when it
is lighter rather than heavier.

Joe Fleming - San Diego