Depends on the size of your case. If the zotac won't fit, go with the gigabyte mini. If it will fit, the Zotac will be marginally better, albiet it will run a little hotter due to blower style cooling.
I personally would go with one that has dual or triple fans and has the highest stock clock speeds that you can afford. The Founders Edition cards tend to run warmer and the fan is louder than the dual or triple fan cards. The mini versions typically only have a single fan that has to work harder (louder) to keep it properly cooled. So basically I can't recommend either. Look for something like a EVGA FTW card, or one of the MSI Twin Frozer cards.
Well if those are the only two cards you are considering I would go with the founders edition card. It likely has similar cooling performance as the mini ITX card, however gigabyte may have cut down the VRM to make the card so small. So if space is not an issue I would say the founders edition card is the better buy, especially since its cheaper.