The Mini wagon will be coming along, but not for another 2 years or so, negating it for your consideration:
http://www.motoringfile.com/2006/01/...ficially-a-go/
Personally, I would go for the subaru. I don't know the engines you guys get in the states, but over this side of the pond, there's the 3.0 Spec B, which seems pretty sweet to me. Although the Mini, in its Cooper and Cooper S guises, are some mean little gokarts. It's a tough choice. Go drive them, is all I can say.