The narrower the tire, the better traction for deeper snow. If you are looking at staying with an all season, I would think you could bump up to a 225/45/17. This should give you better dry traction, maybe better wet, and not much of a difference in deep snow. That should keep you close to the same overall height to keep your speedometer on track.
With all of that, I run a dedicated winter wheel/tire combination here in Minnesota. All seasons tend to be ok for everything but aren't really good at anything. I like the outstanding performance a dedicated winter tire provides, and also upgrade in summer handling a dedicated summer set up has. More of a cost up front, but I am just know having to replace my winter tires, (i purchased them used from Craig's list in 2008) and my summer set is still going strong.