treasure-hunter is right: It depends. They are two totally different beasts. Ie.: there are pro's and con's to each. It's like asking: what's better to drive? A truck, or a corvette? Well it would depend: are you going to be hauling rocks? Might want to consider a truck. Wanna do 140 mph? might want the corvette. Gonna haul kids to soccer practice? may wanna consider a mini-van, etc...
The Sovereign would have the more raw depth, but you will lack all the adjustable bells and whistles that the XLT has. They're also totally different in their sounds, the way you swing, the type signals you want or don't want, etc.... If you are totally used to the XLT, then you may not initialy like the Sovereign.