The Suburbans have two platforms covering MY 2000-2014. Forget about the Tahoe. 2500 Burbs look visually similar, but below the body is a completely different truck.
GMT800 (2000-2006):
Half tons: 5.3 is bulletproof, transmission solid, rear end is the weak link, 4.10 ration available, mine has 195K miles on the original engine and transmission (about 15k of towing). Payload is your limiting factor - around 1500 lbs. A 26-footer is about your max.
3/4 tons: Many will tell you these are the kings of the hill. Especially the 8.1 with the Allison. Absolute beast of a truck. Decent deals around if you're willing to drive a bit. Can find one with 100K for ~$12-13k. They can do 200k easy on the original powertrain. Payload is 2000 lbs.
GMT900 (2007-current)
Both half-ton and 3/4 ton trucks have the receiver integrated into the bumper (part of the crumple zone). Result is a receiver rated at 500 lbs deadweight or 1000 lbs with weight distribution for tongue weight.
Half tons: Early 5.3s ('07-'09) have issues with AFM and oil consumption, leading to early engine failure. Seems to be better starting in 2010. Similar payload to GMT800 - 1500 lbs. As mentioned previously, the GMC Yukon XL Denali (and Escalade ESV/EXT) gets a 6.2 motor - more power, but less payload due to AWD, and no AFM.
3/4 tons: Similarly beastly like the GMT800s, with the handicap of the weak receiver. 6.0 motor and 6-speed transmission are a great combination. VVT gives you a V8 that loves to rev. I love my 08 2500, and will own one until the day I die. 2013 was the last year they were made.