My advice is that if you have a gut preference for one device or the other, if the mini or the Air just feels right, or looks right or makes you smile when you pick it up, go with that. We can list the pros and cons until the end of time, but I think for most it comes down to a subjective personal preference for one or the other. They are both great devices.
And of course if you possibly can, get your hands on each model and try them out for a bit.
And of course if you possibly can, get your hands on each model and try them out for a bit.