I would rule out the Air due to its age
Then the mini 4 which has the benefit of being more portable, but the 2017 5th gen ipad is the newest one so would probably have the longest life span.
The two columns on the right allows you a side by side comparison
Better is a very subjective term. What may be better for you, may not be better for me.
The 5th Gen iPad is the newest of the iPads you list.
The iPad Air was discontinued by Apple in 2016.
If you need extreme portability, you may want the Mini 4.
Otherwise, the 5th Gen is Apple's brand new entry level offering, and has better overall specs than the iPad Mini 4.
The new 2017, iPad 5th generation has better overall specs than any of the iPad models you mentioned.
Latest IPad
