As you can see here, we own both, an '05 Denali, and an '06 H3 Adventure, so I for one have my money where my mouth is. The Denali most definitely outperforms the H3 on the road in every single way, except ONE, and that's cornering. It's far FAR faster, far FAR more comfortable, it's far more stable on the slabwork, it's steering is a lot lighter (almost too light for my taste) It has a really decent turning radius (Don't get me wrong here, the H3 has a really GOOD turning radius, it's just that the Denali's not bad, especially compared to any other full size SUV) The H3's cargo capacity is just about half what the Denali's is. Those friggin' non-flat rear seats do drive me bonkers when I'm trying to carry something back there, at times I've wished I would just take 'em out.
Our Denali gets exactly the same mileage as our H3. The H3 really needs the 6.0, because it's so heavy that when you're in traffic, or driving in the mountains, you've got your foot mashed to the floorboards a lot and the Denali isn't even trying.
I drive straight up and straight down the mountain every day. There's not a straight flat section of road the whole 45 mile commute.
Which one do I prefer commuting in? The H3. I shag the krap out of the sucker. To give you an idea of how bad, the stock tires are gone at 20k. The H3 behaves pretty well... to a point. You can definitely feel the ass end hunting around when you cook a corner too hot, but it does pretty well. I went from the Mini S, an amazing street legal go-cart, to the H3, so I'm pretty familiar with what great handling is. The H3 takes me another eight minutes or so to drive to work. My Sierra 4x4 HD extra cab handles as well as the H3 (believe it or not, the cornering speeds are the same). I've drifted our H3, it does NOT like it. The best thing is to never ever EVER hit the brakes when the H3's out of shape, stay moderately in the go pedal and ride it out, you hit the brakes and it gets more out of shape fast. The heavy rear end wants to move around, and it's not in the direction you're likely to want to go!
The Denali IS mushier than both of those. It's also insanely better on a long trip. I can hurry the Denali on the curves, but it's not happy about it. It takes about the same amount of time in the commute, because it's motor is so much stronger. Going back up the mountain, the Denali is much MUCH more easy and fun to drive because the engine's not screamin at over 4k rpm and the tranny's not hunting every single corner (when I'm hurrying the H3, I just leave it in D3, and quite frequently it shifts down to 2)
This summer, I trailered the H3 up to Oregon on our car hauler when we bought our river house and drove our truck back home alone to work leaving my wife to enjoy the new digs, flew back up, and then a couple of weeks we loaded up the H3 to drive back home. We had that thing PACKED. The roof racks were full, the back was packed to the brim. Let me tell you, I've never ever missed our Denali so badly. Our dogs were miserable.
Commuting, offroading, it's the H3 hands down.
Again, on long trips, it's the Denali. By the way, the Denali is an EXCELLENT snow vehicle. The traction control works wonderfully. The Denali is a wonderful machine, mushy handling and all.
What else would one expect?