The Nokians have very good reviews everywhere I've read about them. Supposedly they even perform well in the dry (ie spring and summer) though they will wear quicker. Stockers were probably Potenza RE-92's which weren't particularly awesome. The question really comes down to what kinda tires do ya want? All-season radials are good for most areas which don't see much snow and very little ice. If you see a significant amount of the white stuff and the clear stuff, you may want to look into a good set of dedicated snow tires.
For my Subaru, I bought a second set of wheels. Good all-season radials (Uniroyals) on the 15" set for most of the year and good studded snows for when it starts to get rough. If you can swing two sets of wheels to run a summer/all-season and winter combination, it'll save ya a lot of time in the tire shop.
The OP's subie probably came with 195/60-r15's stock. You can run several different sizes but that one is pretty decent and not terribly hard to find. You may find it helpful to read some of the reviews of various types of tires at
www.tirerack.com. With it being an AWD Subaru, you'll be able to get going better than most vehicles no matter what tire you're running...however...you also need to stop and turn and AWD can't do any better than a 2WD vehicle with crap tires can.
As a side note, please, for the sake of your clutch-packs and Duty-C solenoid...if you ever need to replace just one tire and the rest are worn more than a coupl'a thousand miles, replace the rest as well. If you don't, you'll increase the likelihood of torque-bind and/or complete loss of AWD capability.