I have a 2009 z71. I previously owned a 2005 and I do consider the 2009 a substantial upgrade in both driveability and comfort. I recommend getting the 2009-14 as opposed to the 07/08 because they have the 6 speed transmission which is much better and more durable than the 4 speed in the 07/08. In my opinion if you want comfort, modern conveniences, and mostly drive on the street the 2015 and newer is the best option. If you want something rugged to take off-road and beat up I would stick with the 09-14. The suspension is more simple if you need to fix or modify anything and there are less electronics to go bad. The g80 rear axle (a lot of people don't like it but I've never had an issue with its dependability or function on any trail) comes standard on the 07-14 z71 whereas I believe it's an option in the 15 and up. I love my 2009 but if I were to daily drive something on the street, the comfort and street driveability of the 2015 is much better. I have driven the 2015 or newer Tahoe's many times as rental vehicles while traveling, including maxing one out at the bonneville salt flats and on some mountain trails in Utah. They are very comfortable and technologically superior to the previous model years. Just my opinion for what it's worth.
This is straight off the chevy newsroom website about the 2009 model year z71. There are quite a few differences with this package:
"The popular Z71 Off Road appearance package returns for 2009. It includes the Z71 Off Road suspension with high-pressure, gas-charged monotube shocks, 18-inch on/off-road tires, automatic-locking rear differential, front recovery hooks, a durable skid plate and a high-capacity air cleaner. Large, color-keyed fender flares, an aggressive front fascia and satin chrome tubular assist steps, and bright chrome front grille insert provide a distinctive appearance.
Inside, a brushed metal-look replaces wood grain accents for a more rugged appearance. Also included are leather-appointed bucket seats that are available in solid Ebony, Cashmere or Titanium."