One deciding factor that may lead you to chose one iPad over another, besides weight and size, maybe also lie with the color gamut of the screen. Anand Lal Shimpi goes over the entire color spectrum pointing out that the mini's display isn't as precise as compared to other similar sized tablets.
photo by AnandTech
The iPad mini with Retina Display has the same color gamut as the standard iPad mini, which is narrower than the iPad Air and less than the sRGB coverage we normally look for. The biggest issue here is that there are other smaller tablets in this price range that do offer sRGB coverage (e.g. Nexus 7, Kindle Fire HDX 8.9).
Within its gamut coverage, the mini’s panel is fairly accurate. A look at our GMB checker test shows performance competitive with the Nexus 7 and not far off the 4th generation iPad. Grayscale reproduction is also quite good. The display looks really good otherwise, but you don’t get the same visual punch you do on the iPad Air.
With this conclusion, are you still a fan? Which size are you going with? I'm leaning towards the Air right now but that's just my two cents.
The Wirecutter on the other hand has declared Apple's new iPad mini with Retina Display its winner for best overall tablet. Of course, if you read PDFs, sheet music or comics, the iPad Air is still the better choice.