My opinion:

• A simple, smooth, realistic and low resolution mesh in the base Geommetry as La Femme:
• A figure only with the essential body groups (easy to work with). Avoid unecessary body groups that most of the times aren't used.;
• Nice and very well made Face morphs and expressions morphs; A nice diversity of Body morphs;
• A figure that works fast!;
• A simple and very well made rigging;
• The UVmap of the figure must be simple, must allow the creation of very detailed Skin textures but with the less seams as possible (The UVmaps of La Femme and Raffael are nice); Don't forget that textures can have a resolution of 8192 x 8192 pixels;
• A professional, good and creative support from merchants in the creation of related products :)

>>> 2nd Face - a cool way to change a figure's face | Renderosity