That's a tough one.....I'm sure there are may opinions about this one. It depends on what you are looking for in a vehicle.
The Denali line gives you AFM free motors from 07 - 09 which are pretty good units. They tend to have piston slap issues from what I've seen, but a lot of the LS motors have that due to piston design and fitment. Generally the noise goes away a few minutes after starting.
10 - 14 have AFM, but you can tune it off. I personally like the power of the newer engine and buttery smooth running, just not a fan of AFM.
I know the early years had some transmission issues to work through on the 6 speed. Again, not all, just some.
Depending on your climate region: 1) hot areas probably have cracked dash boards, but no rust. 2) cooler climates probably have good dash and less sun wear, but maybe rust due to salt.
Mileage has never bothered me as long as the maintenance records showed good care before me. I ran a 2007 up to 227k and sold it. No issues, great truck. Bought it with 160k. Own a 2008 denali I bought with 145k, now has 175k and still good.
Just stuff to ponder. Some good and some bad in all of the years, depends on what you want to potentially deal with as far as repairs or maintenance.