The 2013 Yukon family offers a pretty strong package for passenger duty, although a small third-row seat in the standard-length Yukon--and one that won't fully fold in any of the models--proves an issue for versatility and comfort, making larger crossovers like the GMC Acadia a better pick for most family users who don't need the tough-truck toolkit.
Front seats in either of the Yukon body styles (standard or stretched XL) are fairly wide and flat, and taller drivers will find the windshield header sits fairly low--although they're supremely comfortable. Getting into the seats is more of a clamber than in, say, an Acadia crossover, however. Second-row seats in the standard Yukon have good leg room, but the stretched Yukon XL improves even on that space.
With about 20 inches added to the overall length, and about 14 inches of that devoted to wheelbase (and corresponding to a boost in third-row legroom), the Yukon XL is the way to go if you plan to have regular third-row passengers--provided you have the extra garage-space length. Still, the third row and its high load floor make headroom tight and cargo space more limited than you might think.
As for cargo, the disappointment in all of the models is that the third row doesn't completely fold or tuck into the floor--leaving you to completely remove the third-row seat (a two-person job) if you really need more space. In the standard-length version, there's very little space behind the last row; it has 108.9 cubic feet with the second and third rows down, but just 16.9 cubic feet with the third-row seat raised. With the third row removed and the second row folded, the Yukon XL has a huge 137.2 cubic feet of cargo space, and there's still respectable room for cargo with people in all three rows.The cabin is tight and quiet, though, with fit and finish also top-notch.