The Differences for the Denali would be a 6.0 vs the 5.3, Full time AWD (which will lose about 1-2mpg), but its AWD, and without knowing where you live, just that your vehicles have rust on em not sure how important that is to you… The Denali is leather, with an exterior body kit and upgraded trim. The Denali should have a better stereo than the other ones (if you're an aftermarket stereo kind of person, that probably won't matter). I would ask yourself if that is all worth it to you. Were you in the market for one, or is this doing your friend a favor? Is your friend moving out of the country unexpectedly, or is this something they knew was eventually coming, (as in, did they plan on keeping this thing for a while, and forced to sell it maybe moving because of a family emergency, or did they know they would only have this for several years or so such as with a military move)? Do you know the maintenance history of it? Does it need anything?