The iPad Mini Retina's speed seals the deal.
A lot has been written about the Mini Retina's display. For good reason, of course. Take a display with 786,432 pixels (iPad Mini original) and put it up against one with over 3 million (iPad Retina) and you notice the difference.
But I have been more impressed with the performance of the Mini Retina. After using it for two weeks, the speed is what has sold me.