My wife and I have owned: Yukon, Expedition, and now the Sequoia. There is NO comparison between them. The quality, fit, finish on the Chevy/GMC is unbelievably poor compared to our Sequoia. The Expedition isn't even in the same leage. A regular Yukon has a horrible 3rd row and NO space behind it. My wife is a Realtor and has had 7 people in the Sequoia with comfort many times (I'm 6'3" and sat in the 3rd row for about 2 hours, no problems, very comfortable).
We did drive the Yukon XL and liked the room inside but HATED the way it drives. Talk about driving your living room down the street. Visibility is poor, turning radious is terrible, it feels so big it's uncomfortable to drive, quality is poor (certainly not in the same league there), the design is very outdated (all the Chevy trucks are getting hammered in the magazines now because they're not up to the standard until their redesign), gas mileage is rediculous (real world my wife gets 16-17 w/ the A/C on, she got 13-14 with our "lighter weight" Yukon which has A/C that can't keep up in the Arizona summer).
Sorry to sound so harse, I should make it out to be a horrible vehicle, but an unbiased opion (as we've owned them): there is no comparison...