I've actually been using ContiExtremeContacts myself. I've been using them ever since I bought my car and changed out the OEM(OEM were some Toyo tires that Nissan selected for their 99' Maxima SE-L model). The tires are nice for the New England weather. A definite improvement over the OEM when it comes to rain and snow. However there are some cons to the tires. They do tend to flatspot if you leave the car parked for awhile, but will go away in 10-15secs or so of driving... but nevertheless, it is there. The Continentals also produce a bit more noise. The pros are better handling, and traction basically.
I've never used Nokian WR's, so i'm afraid I cannot comment on those.
- hito