[HummerMann]

I've got an '06, I bought new and have been very happy with it and had an 03 too. I have the air suspension, and it is doing fine and I love it - so far no problems. I also have the factory nav which I like and have found people having electrical problems with some aftermarket navs.
As for '08 and newer vs '07 and older, I like the power of the newer ones, but they also like premium gas. Also, the 08 and newer 6.2s have less torque below 2500 rpm than the 6.0s which might be a towing factor to you. I think the seats are more comfortable in the '07 and older, but I like the dash on the 08 and newer and padded center console. If you use the back seats and get an SUT they took out the back seat variable air ducts on the '08 and newer. Do the aftermarket wheels and tires yourself. I loved the gobi rack I had on our '03, but it would never fit in the garage after that. Personal observation is that 06 and 07 have less electrical problems than 05 and older.