Sounds like the 2013 model may be the one to go after. It was the final year with the 5.0 V8 motor, which has proven quite reliable and a nice match for a vehicle of the LR4's weight.
The LR4 also seems to be the model within the Land Rover lineup that experiences the fewest mechanical issues. So with the articles and comments you read on Rover reliability, you have to keep that in consideration, and it should help boost your buyer confidence a bit.
Regardless of which year you choose, it sounds like most buyers are more than pleased. The trucks are nicely refined, quiet, rare in traffic, and can tow with the best of the SUVs.
We bought a 2013 because of the comments I read on Forums and articles here and in Great Britain's press. Couldn't be happier. The engine and how it motivates the vehicle is probably the highlight. Especially in Sport Mode! But there's a lot to like. The high, commanding sitting position and the seats themselves. The fantastic fat and well cushioned steering wheel. The sound system. The smooth ride. The space for 3rd row passengers when needed. The size of the vehicle compared to some other 7 seaters which are just a tad bit too big like Escalades, Tahoes, and such... A lot to like...
Also of note, it sounds like the Nav system from 2012 and earlier also had quite a few issues that they seemed to iron out starting in 2013. It's not the most intuitive system in the world but it's decent and is easy to learn. If you're currently driving something pre-2006 when the Bluetooth technology became mainstream, it should be something you'll also enjoy tinkering with.
Go for low mileage if possible. Perhaps a warranty if available. But it's really not a must in my mind. If you can afford the truck, you can probably afford an occasional $800 or $1000 bill for a big repair. If you have a good independent mechanic, he can do the work at reasonable prices and make the truck way less expensive to own. For instance, you'll read about $2000 brake jobs, but it can easily be done on all four corners for under $600, parts included. My mechanic charged me $550... I just had an oil change and my mechanic charged me $35 for the filter and labor. I supplied the oil from the LR dealership which cost $7.50 per quart and it took 8 or 9 quarts. I bought a dozen for about $95 so I have a few extras for when the oil gauge shows it needs a little.
Set aside a couple grand for that rare day when your truck might fail you, and if it never does, you won't have spent a dime. Buy a warranty for 3 or 4 grand and you'll never see that back if the truck is one of the 80 out of 100 that is problem free. If it's one of the 20 problematic examples to come off the manufacturing floor, you still might not spend $4000 in repair costs. So do your research, buy wisely, and keep up on the maintenance. You'll likely be good. I had warranties on BMW's I previously owned and never got my moneys worth out of them. This is the story you hear less often than the guy who's ****** that he had to spend $3000 on a whole new suspension system or something exotic and he's online warning every prospective buyer to watch out. Manufacturers and dealerships sell warranties because they generally make money on them. If the cars were really as unreliable as some might say, they'd never offer a warranty in the first place. It's all about revenue, not reliability. For the most part, cars are more reliable than they ever were. Choose a good one, develop a relationship with a good mechanic if you haven't already, and don't look back...
At first my mechanic told my wife he wasn't too thrilled to be working on a Land Rover as we're in the Midwest and he sees predominantly Domestics. But he said the same thing about my Audi S4 and VW's too! And he's been golden on them for years, so I pushed him a little, and bribed him by buying him the only LR4 specific tool he'd need to work on my truck: An oil filter removal tool which cost me $20 on Ebay. So don't let the brand name scare you thinking that you can't get reasonable service done by reasonable mechanics.
Good luck...Let's see the pictures once that bad boy arrives in your garage!