Depends on how much snow/ice you encounter. The Extreme 294s are great for really severe conditions such as glare ice after the snow has melted and re-frozen on road or off or if the snow/ice is really rutted, but there is a serious price paid in rolling resistance. You could however ride across a moist hockey rink or frozen lake with little difficulty. I only pull them out when most car drivers can't even navigate the roads or when I am riding frozen trails/downhills that are slippery even in non-frozen conditions.

The Mount and Grounds have much less rolling resistance and if the roads are really icy, but not so bad that it keeps car off the road I just drop the pressure down to 40-45psi and go on my way. Its nice to have a choice, but if I had to pick just one set I'd probably take the Mount and Grounds because under normal winter conditions they work fine. The Extremes are really not necessary until conditions are so severe that most people won't even consider going outside, but I want the adventure.

My experience with Schwalbe Marathon Winters is about the same as the Mount and Grounds, but I wouldn't even consider any of the other brands (i.e., Innovas and many of the cheaper brands carried by REI et al) because they either use steel rather than carbide studs or they just don't have proper distribution of the studs.