Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
The Air 2 has a three core A8x cpu while the mini has a dual core A7. Air has 2gb of ram while mini has 1. Also the screen has a better screen
 
The air 2 is also thinner and has a more powerful gpu unit. The screen also seems more solid to type on. I have both and i would have not bought the air 2 if it wasnt for the small capacity of the mini (16 gb) as it is performing well and im not having the lag problems some users are noticing. The mini also has the perfect size. Having said that, the air 2 is a beast and should last long.
 
The Air 2 also has better speakers. The Air 2 has finger print id, but of course if you really want that on the mini form factor, you can get the mini 3.
 
The Air 2 also has better speakers. The Air 2 has finger print id, but of course if you really want that on the mini form factor, you can get the mini 3.

No reason to pay more for the Mini 3. I have the Mini 2 and am waiting for the next one, which will hopefully have the A8 or even the A9 chip. If it has the A8 I'm not sure if I should upgrade.
 
Just wanted to add one more thing to the discussion. I have both a mini 2 and air 2. I have been disappointed in the air 2's battery life. The mini 2 is like the energizer bunny - it just keeps going and going. I can get 12 hours easily over 4-5 days of use but similar use with the air 2 will only get me 8-10 hours over 2 days. The mini 2 can also be handled with one hand. I can "palm" mine and carry it around almost like a big cell phone. It will also fit into the pockets on my shorts and some of my pants, and the pocket on hoodie sweatshirts. The air 2 cannot do these things, or at least not easily.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.