I think the EXPED UL7 would be a more comfortable mat than the Xtherm. I have the Xtherm and it's very warm, but it's a narrow cut. I sleep directly on snow at least once a week and it's been great. My original Neoair only has an R-value of 2.5 and that was too freaking cold so it's only used in the summer. As for the crinkling, it sounds loud in the store, but in real-life use, I haven't found it to be an issue. The UL7 would be quieter. Most of my winter camping is now done with the Xtherm and a WM Alpinlite - it's a very sweet lightweight set-up. I decided to go with the Xtherm over the UL7 only b/c it was lighter and substantially cheaper. So far, I've been very impressed. The inc. pump sack works very well as well, once you get the hang of it. I also have an EXPED DM 9 which I occasionally use. It's ridiculously comfortable and warm, but it's expensive, bulky, and heavy. I purchased it more for base camp type camping.
Pros Xtherm: lightweight, low bulk, warm, cheaper than UL7
Cons Xtherm: narrow cut, probably delicate compared to others in this category, noisier [though I haven't found this to be an issue]
Pros UL7: wider, slightly warmer than Xtherm, very comfortable given the weight
Cons UL7: expensive, heavier, bulkier, more finicky.
Both companies have excellent warranty/customer service. I've had to replace an EXPED DM 9 and they were excellent. I've never had a Therm-a-rest product fail on me [and I've owned 5 different models], but I have dealt with Cascade Designs in the past.
If the price doesn't matter, I'd go with the UL7.