By now, we've already compared the iPad Air 2 with the iPad Air and the iPad mini 3 with last year's iPad mini. But what we're trying now to do is to try and see which product should you buy from Apple, if that's what you intend.
First of all, it needs to be made clear from the beginning that, from a purchase perspective, the single big difference between the iPad Air 2 and the iPad mini 3 is the screen size. So, if you are more comfortable with the 7.9 inch version, then it's not worth comparing it to the bigger one and viceversa. It all boils down to taste.
However, if you don't have a specific size that you'd like to choose, and you just want to see wich is the best product, here's a brief and concise explanation that you need to know.
The iPad Air 2 is a much important upgrade to the iPad Air than the iPad Mini 3 is to the iPad Mini 2. That's why I recommend getting the 2013 iPad Mini, which is cheaper by $100. The iPad mini 3 has the gold color option, the TouchID fingerprint reader and that's about it.
There are new storage options, which is nice, but you'll have to pay extra for more. This is a clever strategy from Apple to increase their profit margins. While the consumers perceives the jump from 16GB to 64GB as big and worthwhile; on the paper, for Apple $100 per sold product is important.
Between these two, the iPad Air 2 is obviously the product with bigger improvements - it has the newest A8X processor which is quite powerful, comes with an improved 8MP camera, has a new Burst and Slo-Mo mode and its display has been improved, as well.
But it is also more expensive by $100. However, in this scenario, this upgrade seems justified - you get better performance, a thinner gadget, better pictures and a better build. So, naturally, the iPad Air 2 should be the winner. But, then again, if you like the iPad mini 3 better, then that's alright. It's all about personal choice.