Another thing to think about is are you planning on being nawhtey. Some skin lines have fabulous makeup (starley's Vogue skins come to mind). While others might be more limited in makeup styles, but look gorgeous naked.
It took eight months for me to settle on a skin and shape. I settled on what I'm wearing now because of how the makeup looked on my face. At the time I didn't give much thought to how it looked naked. My only complaint now is that it does suffer from the 'dirty bottom' effect due to the shading there. Now I don't plan on changing either one. Of course there are more makeup options for this one that I don't have yet.....
For reference, it is the Skin Within Adhira freckled.