Really? The Tab 10.1 is taking a lot of heat for having a half baked build, lots of browser crashing and looping being reported at XDA. The Tab feels like it has decent build quality, for a Samsung though. Be warned though, it lacks an sd card slot and will be getting TouchWiz(gag!) in an upcoming update.
I haven't handled a Thrive yet, going to go that soon, but I'd put the Iconia on the bottom. The Xoom is a far better device than the Acer, its major downside seems to be the mounting the sd card bug, fixed in 3.1 for European Xooms and in 3.2 for US Xooms. I don't understand the flak the Xoom takes for allegedly having a bad screen, when the iPad gets praised for having a good screen because the two devices put up similar numbers in brightness and blanks.
From what I could tell, the Tab 10.1, Transformer, and Xoom all had comparable screens when I checked them out with some light web browsing and YouTube videos.
Anyone considering a tablet though, really has to go put hands on the actual product before they buy one.