I replaced the OEM Goodyear Wranglers on my Jeep Grand Cherokee with the Michelin LTX several years ago and they were much better. At the time the Jeep was used in heavy snow in the mountains and the Michelins handled it well- but they are quite expensive. I also had Bridgestone Blizzacks on another Jeep and they were exceptional in snow and ice, however they wore quickly on dry roads and handled poorly in warm weather.
I just received the Pirelli Scorpion M/S for my Touareg and haven't used them yet but they appear to be a good design and have received good reviews. They are reasonably priced at Tire Rack, and they also sell the BERU sensors for the TPMS. Hancock does have a good reputation but I have no first hand knowledge. Whatever you buy make sure you get the proper load rating, XL or "Extra Load" to handle the T-Reg's weight. The 255/55-18 size looks good, I wouldn't go larger or smaller, unless you are going to be in a lot of deep snow, then I might use 235s.