The 2013 has much nicer specs but many people have had tons of issues with it - I personally have bought and returned three of them before giving up. The first one had major ghost-touching issues that made the on-screen keyboard effectively unusable every now and then, the second one started randomly rebooting after a week, had GPS issues, loose USB port, minor ghost-touching and the third one started freezing and rebooting multiple times per day almost right out of the box. That's three unusable devices out of three and they were purchased about three weeks apart from three different places.
I own a 2012 model and it started having stability issues after I upgraded it to 4.3. Not sure if that is the hardware "getting old" or if it is a software thing - I certainly would not expect a one year old tablet to start dying and on the N7 forum, I am not the only one who has been having stability issues with their N7-2012 after 4.3.
So, as a former owner of N7-2013s and current owner of a N7-2012, I do not think I would recommend either one... as tempting as the N7-2013 might be.
I would wait for the N9 and hope it fares better reliability-wise than its two Asus-made predecessors.