i have both and latest iPad Air
i received a gift this year to spend on tech and got an iPad Air, a Nexus 7 and a 7 Fire HDX. (i could get both N7 and HDX for price of iPad Mini) I'm pretty much an apple fan-boy (i've built 3 or 4 hackintoshes, have a MacBook Pro, wife has an MBP Air, Apple TV, and airport's around the house for whole house music). i love the iPad Air - by far the finest piece of quality tech of the 3, but i seldom take it out of the house.
to run around with, i'm finding myself reaching for the N7. So far, I've had none of the QC issues that some sites are reporting. the stock interface i'm finding more useful than even the iPad Air, with the widgets and such. the OS is still not as bullet-proof as iOS, nor quite as smooth. but, it's come a long way from the first couple of years.
the HDX also feels like a quality piece of gear. the guts and specs are amazing. i really like the feel of the device, love the screen, the sound, and even like the button placement that others have complained about. i love amazon (have a prime membership) but FIREOS sucks. it's just not as intuitive and useful of an interface. the only person i'd recommend this to is someone who is totally new to tablets, only wants to view content, and is not tech davy. with Mayday it's basically the perfect device for my 77 year old mom. i'm going to hold on to my HDX for another month or so in hopes of a better custom ROM, but if nothing comes up it's going up for sale on craigslist.
if i could have only one, i'd have a really hard time parting with the N7. for the price, i think it's the best deal going.