I came at the used Jeep thing from a different angle. The resale is so frickin' high on these things that I think you really have to do your homework to make it worthwhile to buy used. I say get a '12 and deal with the higher payment. You'll get some of that back in gas money, some of it back in repairs. It will still cost you more, but not as much as you might think at first.
FYI I put my money where my mouth is -been looking at new and used JK's for 2 years and finally bought a 2 door '12 Rubi last night. I just looked at all of the different factors involved in cost of ownership and came to the conclusion that a new one, while clearly more expensive, isn't *that* much more than a used one unless you make a very, very good deal on a used Jeep.
That said, if you are set on a used Jeep, I agree wholeheartedly with kjeeper10. Low miles, factory warranty, Jeep dealer. I would add that you should buy from a dealer with a good reputation and ask to see some maintenance records.