If you spot an '05-'07 TB or Envoy with low miles, clean, no wrecks, regularly maintained, you're likely to get good service out of it for quite a while. GM had fixed most if not all of the earlier model year bugs by then. The standard powertrain is an aluminum 4.2 L inline 6 cyl w/ 4 speed/overdrive auto trans. Unless you honestly need 4 wheel drive the 2 wheel rear drive is ample and less-than-half the potential headache. It's a mid-size SUV on a Chevy Silverado/GMC Sierra P/U chassis. Buick Rendezvous is a mid-size crossover with a V-6 (3.6 L, I believe) and front-wheel drive. I think the TBs/Envoys were better overall. It'll soon be moot, as GM will be phasing out those vehicles in favor of its new generation of crossovers, Buick Enclave, GMC Acadia, Saturn something. They're pricey, closer on a par with the Lexus crossover SUVs.
You can make a good deal on a used TB or Envoy right now from an individual or coming off lease at a GM dealer's, if you shop carefully.