How should i chose my guinea pigs? Im buying them from Petsmart?

I'm getting two guinea pigs tomorrow,two girls. I don't know how to pick them! Should i pick the one that is the nicest or cutest? Or the one that interests me the most?? Or should i know the info about them, like how old it is, and which guinea pig the pet seller would recommend? Please give some tips! I also have another quick questionwhich is better to use in the cage fleece or bedding?