If they will keep it a long time and a bigger screen seems their type, I'd go with the iPad Air 2. It's the best deal right now because of the 2GB RAM.
Now if they don't seem like they want a bigger screen and specs or being future proof would be their least priorities, a Mini would be good.
I got a Mini 3 because I wanted more storage space and I didn't want to buy refurbished. I'm enjoying the touch ID and I've had no trouble with it at all. I had the original Mini and don't like bigger screens.
Good luck!