I have a POD Pro but haven't messed with the XT version so I can't give you a direct comparison. I have heard others say that the XT has superior effects, but the actual amp tones of the original Pro were superior to the XT.
I will tell you that I love my POD Pro. I only use it for practicing and getting ideas down at home. I think it sounds fantastic, it is insanely versatile and I love being able to go pure digital direct to PC. I really can find very few faults with it. The effects are pretty bare minimum, but they get the job done reasonable well. With the new XT out now, these are popping up used for great prices...I'd jump on one over the XT just on that alone if I were you.
For live playing, I used to run it through a mesa 20/20, a g-major and mesa 2x12 cab. Found it a little flat sounding, added a BBE sonic maximizer and that helped but still wasn't as "pure" as I would have hoped. Long story short, dumped the rack stuff and now just use pure tube stuff live. But I kept the POD Pro because it is such a great tool for rehearsing and recording quickly and easily with great sounds.