Never owned a Ford 5.4, but we have liked our Suburbans. Our '05 was a good vehicle, towed OK w/ 4.10 gears.
Our 2010 is much better, however -- the engine has a bit more hp, is much smoother to the point you don't mind letting it rev a bit, and the 6 spd transmission is a major upgrade over the 4 spd. We test drove similar year Expeditions as well, seemed similar, but we liked the GM better. Seemed to drive and ride a little smoother, plus we were familiar with it. In all, our 2010 Suburban is one of the best vehicles we've ever owned.
Driving '10 and '11 Expys and Suburbans back to back, it didn't seem to me that one outperformed the other from a power standpoint.
If you get the Suburban with the right equipment, it has decent ratings -- our 2010 is rated to tow 8400 lbs or something like that. Deals with our 6k lb travel trailer just fine. It is a bit hard to find, though -- the volume seller seems to be the 3.08 gears and a paltry 5000 lb tow rating.
That said, I'd wait for the 2015 Expedition EL Ecoboost! More than likely will be our next family hauler.