I'd vote no on the air suspension, because when it does break, you'll be hunting parts and burning time/money tracing down the problem. For now, most everything is still available, but that won't last forever. The coil suspension on the other hand will likely last the life of the truck. As the tag line went, "Hummer: It's like nothing else", and that goes double for parts. Once you get into secondary systems and body, there's not a lot of crossover from the GM parts bins, and things start getting expensive.
If I had it to do over again, I'd buy a coil-spring truck without the sunroof, instead of the H2 Luxury I bought. I'd also give serious consideration on whether or not I wanted the Bose stereo option. It sounds great, but if you decide to replace the head unit, you are looking at a ~$80 cost for the adapter cable to connect a standard head unit to the Bose amplifier. When you're stepping down to a regular single-DIN unit to free up a slot on the center stack, that $80 comes darn close to the cost of the head unit.
As to weak points, the front ball joints, the tie rod ends. the sunroof, the transmission, and on the 08-09 the oil pump in the engine. Also, for all intents and purposes, you're looking at the 08 only. Less than 1000 (closer to 600, IIRC) were built in 09, so they're going to be rarer than hen's teeth.