I've had two friends at work buy JKUs in the last two months.
One has been "window shopping" for that last 4 or 5 years... and I'm not kidding. If you're looking for used, often the best bets are buying a local rig that will have a service history at the local dealer. You can ask the service dept to pull up the VIN and they can tell you what was done and when. If it had new heads put on it, they can tell you. This one friend would ask me questions from time to time and would often send me links to JKs for sale. MOST of the time, I could tell him that what he was looking at was only 4-5k under the price of a new one. He was also looking for a Sahara with a lift and 35s. That was his minimum standard. Beyond that, he was completely open. So after about 5 years, he finally located and purchased a JKU Sahara. A brand new 2016. Within two weeks, it was on 3" of lift and 35's. He still has invested only about 2k over some other used 14/15 JKs.
The second friend had a 2010 JKU he bought new. For whatever stupid reason, his wife talked him into trading it in on a Ford Flex and hated it. Then they fell into a bankruptcy that they just are now getting out of. They found a stock 2014 just last week. I have not been told what the price was, but knowing their history, it had to be a VERY solid deal for them to afford it.
Your buying experience is going to weigh heavily on where you're making your deal and how excited you are on the purchase. I've had good and bad experiences at the dealers and only one good one when buying used. I say only one, because some people just felt slightly dishonest when we talked about the car/truck. The last two vehicle purchases were both good and bad. The good one, we were buying a new Ram 1500. The dealership experience had been so-so... a nice sales rep with a very pushy and overly excited sales manager.... however I had the truck about 5k under sticker and with my trade I was walking out with a new Ram for $27,000. The not-so-good one was the used Challenger I bought my wife last July. The dealership knew absolutely nothing about Dodge which bugged me, and after we did a walk around of the car before the deal, I found a cracked taillight that we obviously missed. The dealership replaced it, but not without a LOT of back-and-forth calls and chatter. The icing on the no-so-good feeling was I've never carried two car loans in my life.... that honestly took away some of the excitement. But remember what I said about how much you like the car? I called my own bank and secured my own loan. I walked in with a check and walked out with the car.
I have State Farm, who has their own bank. I've bought two cars and one boat with them and I can't tell you how supremely easy it was and how competitive the rate was. Doing it that way has relieved MANY of the issues that have sucked the life out of auto purchases at the dealership. My first experience like this was buying a Fiat 500 Abarth.... which was an amazing car. I got an awesome deal on the car and walked out in an excited daze. Sadly, they retain practically NO value and the dealer network is horrible... but thats another story... sorry.
I guess my thought would be, if you're looking used and you are familiar with the JK, shop used from owner. You will find your best deals on Jeeps that way (at least in the south east) and if you have your own bank its pretty dang easy. At the dealer, its easier to make them do the work to find a loan that works for you if you don't have a bank. If a warranty is a factor, then the newer the better.
I recommend the '12-up because the engine/trans combo is better than the '07-11. Sure, I have a '07 JKU Rubicon with 67,000 miles on it. Its starting to show its age, too. Jan 22nd is its birthday..... it'll be 10 years old.
I'll also point out that this overweight under powered JK has been to NYC twice... Durango, Colorado... South Florida... Central Florida... OBX.... Camp Lejune... Tennessee... Alabama...
So even being the wheezy fat pig that it is, it still gets down the road at interstate speeds with the family and luggage. Those 67,000 miles have seen the smokies and the rockies. The Atlantic and the Gulf. Times Square and Ouray. So long as its in good repair it will take you where you need it to. Except past a gas station.