Acre or Iris for one great meal in Memphis?
Iris is far and away #1 for me. You do often need to make reservations 3 or 4 weeks out there for a weekend. It's pretty small and they try to do 2 seatings or so. They do have several patio tables and I have seen them empty before. So it might be worth showing up as a walk-in and seeing if something is available. But if you're coming from out of town you might want more confirmation than that. After Iris, I have trouble picking a clear #2. I used to like Erling Jensen a lot, but it is a more "old school" style of place and cooking than several of the others you hear about. Haven't been there in a while. In addition to Acre, Interim, Bari, and Andrew Michael are other favorite nice places that would probably come up in the conversation - at least for me.
Incidentally, Andrew Michael's cheaper / casual offshoot Hog & Hominy has been getting the best press in town lately, including several national pieces.