Probably Target Field because you cannot sell alcohol at TCF Bank. And we all know we are gonna want our brews when watching an outdoor game in the winter.
Not the only reason. Traffic would be an absolute nightmare at TCF Field. Two 1-way roads on either side, and I-94 and I-35W come off on opposite ends of those 1-ways. Lightrail isn't finished yet either. Doesn't tie in where are you going to park all the cars at? Especially if the roads are terrible and the plows haven't gone through or blocked the side of the roads too much. When I went down to the Vikes game there, you couldn't park in any of the ramps around the field because they were reserved for media, players/families, VIP, etc etc etc.
Target field eliminates almost all of this. Roads are at least 2-3 lanes as well helping alleviate traffic congestion. Plus yes, the alcohol thing helps.