Here's my take on snow tires. I live in Truckee CA; we have snow on the road most of the winter. I switch to dedicated SNOW TIRES, on stock rims. SNOW's are MUCH superior to mud+snows, as fitted to many vehicles.
If you are on snow for more than 50% of the time, a studless ice tire like the Blizzak WS60 is the best. If you are only on snow zero to 20% of the time, get a performance snow tire like the LM25.
I go down one width size with snows. See the size chart diect from Bridgestone for the WS60's at:http://www.bridgestonetire.com/tires...roduct_ID=2007
When going down in width, select a size that is as close as possible to the 'rolling diameter' or RPM (revs per mile) as your stock tire.
Tirerack has all you want to know about winter tires. They have many real test results at:http://www.tirerack.com/winter/wintertesting.jsp
Check the 'The Continuing Revolution in Winter Tires ' athttp://www.tirerack.com/tires/tests/...ay.jsp?ttid=65
They also have recommendations for down-widthing.
Tirerack also has customer survey results at:http://www.tirerack.com/tires/survey...sp?type=W&VT=C
The WS60 comes out best for dedicated 'studless ice and snow' tires.
Check their site also for comparisons of 'studless ice and snow' versus studed tires. The studless ones win. Studs are only good on ice, and don't help on soft snow, and the studded tires they tested where worse that the 'studless ice and snow' even on ice.
Remember that snows are generally softer than standard tires, so they wear quicker, and will be noisier.
Thats my 10c worth!!! - hope it helps