If you're after a Nexus tablet, from this point on you'll need to be OK with the Nexus 9, because that's the only one that's still up for grabs from Google's official hardware store. The 2013 model of the Nexus 7 made by Asus is no longer available for purchase, as it's been discontinued after a pretty long run - it was announced in July of 2013. You can probably still find some Nexus 7 (2013) units in stock at other retailers, but if you want one of these you should act fast, because once they're gone there will be no more. Otherwise, you can pick the Nexus 9 by HTC, and hope that Google will finally release Android 5.1.x for it...
Source: http://www.gsmarena.com/the_asus_nexus_7_2013_tablet_has_been_discontinued-news-12037.php