You can get the ipad air 11 inch for 549 with a 100 dollar gift card back. So under 500 dollars.
If you lay in bed and watch video or lay in bed and type on forums it is the best deal.
The other two cost a lot more and you do not need more than the base 128gb ipad air.
if you have more needs scale up to the ipad with 256gb .
if you have more needs switch to the ipad pro.
in all cases i would say the the cheapest one to fit your needs is the best one for you.