I have stores at all three places. Zazzle is the best for prints and greeting cards, but you can't set the prices like you can on the other two. (It's just a flat commission percentage there) Cafepress is the best for product options/selection, but it's really not worth setting up unless you have a premium store. I suggest setting up a Zazzle store for prints, cards, and mugs and use Printfection for clothing, etc. Printfection doesn't have mugs otherwise I'd say just go with them. Let me know if you need help.
