Me, I'm going for the 32GB (WiFi only), not sure about color quite yet (tick TOCK on that, eh?)
Why 32GB? Usually I follow "go big or go home" on storage, but I am also upgrading from my iPad original to a 4 and wanting to do it this fall, although not in the pre-order period. For the larger device, I'll spring for the 64GB. I just can't go big on both this fall.
So, my pick for the iPad mini storage size is about a budget constraint, tempered by the knowledge that I lived in 32GB with the iPhone 3GS and it worked out OK (although I went to 64 on the iPHone 4S).
I want this mini tablet size for ease of reading books. I expect also to refresh some selections of "new to me" music on it, and maintain a fairly stable collection of certain music plus revolving picks of old favorite movies and TV shows. Not many apps short of a few utilities and mail. Not spreadsheets and databases and other space taker-uppers like my magazine and newspaper archives, that stuff can stay on the larger iPad and laptop.