Of the subies, I think the smaller is better: impreza / outback sport > forester > outback.
I have the 2.5 impreza Outback sport manual for 5 years and like it alot for both canyon driving and cruising the wasatch front.The 2.5 is enough for the smaller car and feels pretty well balanced. Adding ~50-75 hp and torque this thing would fly so the WRX maybe in my future. The only big problem is a lack of cargo space, but a roof box does help, still a long camping trip for a couple of people is very tight, even with the roof box full.
I tried the forester, outback, and impreza / OBS at time of purchase (2008) and the other optiosn were not impressive in handling in the canyons and mountain roads.
I have tried newer outback V6 (2010) on a trip to Pitsburgh and drove to DC and back over a week or so and still have the same impression handling wise. Its a good interstate car, but for mountain roads or city streets, I prefer the handling of the smaller cars. I think the V6 they offer is required for a decent car (I would not get the 2.5 for a car that will be driven up hill).
The new forester (2011) is a a big improvement over the prior model handling wise. I drove the 2.5 non-turbo model for a week a trip to Appalachian mountains. I think with a turbo it would be nice, but with he 2.5 its still a bit lacking in a midsize vehicle.
Edited by tromano - 8/25/12 at 2:45pm
On forest roads, the OBS has is a family car with 5.5" clearance. It does very well for graded dirt and light mud. But in chunkier sections, its going to get beat up quickly and I would not take it off the roads and keep off of anything like an ATV trail. The only benefit for a smaller vehicle is that you have more room to pick your line and follow the smoothest path you can find.