I located this today and thought it could be relevant.
The 16GB LTE Sony Xperia Z2 Tablet costs the same as Apple’s equivalent iPad. Apple does offer a 32GB cellular model, at 579. Other options include 64GB and 128GB Wi-Fi only- and cellular iPad Airs. These range from 559 for the 64GB Wi-Fi iPad, up to 739 for a 128GB Wi-Fi and cellular iPad Air. So there is more variety in the iPad Air range, but if you want a 32GB Wi-Fi-only tablet the Xperia Z2 Tablet is cheaper. One other thing to consider: a quick online search suggests that if you shop around you can get the Xperia Z2 Tablet cheaper than you can the iPad Air.
Initially found at: http://review.techworld.com/mobile-wireless/3514688/ipad-air-vs-xperia-z2-tablet-comparison/?olo=rss