As I Jeweler, I've really come to appreciate the pro's of a lot of different designs. Maybe I wouldn't prefer them for myself but I LOVE to work with unusual cuts. For example:
*Shapes with more "length" (Pear, Marquise, Modified Rectangular Radiant, Shield, Dahlia cut, Long Hexagon Cut, Lozenge, Romboid, ect) can often be more comfortable to wear on a finger than "fatter" styles and are a preferred option if you want a lot of side stones or a "big" look. If you are going to do a microset halo on a larger stone... it would be easier with a Marquise or Pearshape vs a princess cut.
*The unusual cuts (fan shape, horsehead shape, asscher, grace cut, ect) can usually command a nice premium price but can be a little harder to sell fast.
*Round shapes sell easy and are always in demand.
*Old or "out of style" shapes can often be reset to look amazing and modern, even by simply flipping the stone to a different angle.