Offroad ability=traction+clearance. The devil is in the detail, of course.
So...I will put it like this.
Traction A: keep the wheels moving:
1/4x4/efficient AWD (Subaru).
2/True locking center differential/effective enough CD (Subaru)
3/ABS-based traction aid (VDC. A-TRAC, BLD, whatever you wanna call it). Enough in most cases. Not enough in rock crawling. Remember, on a Subaru VDC is NEVER off. What is OFF is the function that cuts power to the engine.
4/True rear locker (used all over before VDC systems, used for rock crawling in vehicles with VDC).
5/True front locker. Extreme rock crawling. More uses on older vehicles with no VDC.
Vehicles with good low range and no true rear or front lockers like 100-series Land Cruiser (USDM) and 2007+ non-Rubicon Wranglers can still make it through very serious ledges thanks to A-Trac (Toyota term) or BLD (Jeep term for VDC). However, you still want those traditional lockers for extreme terrain or for frequent visits to difficult trails.
Traction B: controlled movement over harsh terrain:
1/ Auto with a powerful engine, at a minimum
2/ Low range
3/ Better low range, crawl ratio. Crawl ratio is a big topic for 4x4s.
Subaru offers nothing anymore. Toyota is generally about 2.7:1, as most Jeeps. The Rubicon, however, is 4:1. It can basically idle over crazy stuff.
Clearance. The thing about clearance is that it is not just about minimum clearance.
Clearance A: Minimum clearance
Minimum clearance is what rock you can straddle on otherwise flat terrain.
Solid axle 4x4: your differentials, usually a bit more clearance under front
IFS 4x4: usually the rear differential cover but on the GX 470 (US Prado derivative), it is actually at the front.
Subaru: pretty nicely tugged oil pan and nicely high rear diff, but highly exposed exhaust along length of car.
Clearance B: Relative clearance
This is the clearance that matters most. It is a matter of minimum clearance in relation to wheelbase. The longer the wheelbase, the more clearance is needed to go over stuff. I am not just talking brakeover angle, as in cresting over something. I am talking the ability to drive over undulating terrain, rocky or otherwise. Old Wranglers, and some more recent ones, the entry level trims, had modest ground clearance, but they could still drive over tough terrain because of the short wheelbase. Ditto Samurai. This is also what makes the old Foresters so successful off-road. They start with very modest minimum clearance and even with the typical 2" lift they cannot get really high. But the short wheelbase works wonders in harsh terrain. Actually, the 2009-13 Forester should also be as good since it starts higher and its AA/DA are better.
Clearance C: Rocker Panel height
This is one reason why Subarus are so hopeless in rock crawling. With a 2" lift and oversize tires, I get to a respectable 12" real life rocker clearance with aired down tires. But this is the bare minimum needed for many moderate 4x4 trails. This is less than half what modified Wranglers have. True, boulder-crawling is not the name of the game everywhere, but it often is in my corner of the woods.
Clearance D: Approach and departure angles
Subaru: 18-25 AA for stock
Gentrified 4x4: 23-28
Typical 4x4: 28-32
Wrangler: 40 and up.
Your Subaru winner here is the 2009-13 XT Forester. Generally, with a lift and better tires, all Foresters are going to be okay or even good. But the other Subaru models are a joke in this department. The absolute minimum needed AA, judging from my experience and from what Toyota did to its gentrified GX 460 in 2013, is 23 degrees. Everything less is simply forgettable. And 23 is barely enough on many moderate trails. There is a reason OB owners do what not to their bumpers.
DA is not quite as critical and a hitch can protect a vulnerable bumper (to a point).
Clearance E: Brakeover angle.
Most: 20sh these days, bare minimum
Good: 23sh
Best: 25-27. But you have to go to 80-series LC and 2dr Rubicons for these numbers.
I forgot what mine is now (22?). I lacked BA once, when I went up an optional rocky face, not noticing how sharp the top was. Oops. Not sure what I hit, it was a good hit but have not seen consequences.
Clearance F: Front bumper, AA, and front undercarriage
This is like relative ground clearance. Here is what I mean. The worst thing about an OB is the front bumper, right? But you can rephrase this as the best thing about an OB being the front bumper. Why? Because the front bumper is so awful that it acts as an early warning system. Chances you can go over a rock that later impales your oil pan are slim to none. But consider the USDM Nissan Xterra in its regular 4x4 trim (it has a better one). In this more common 4x4 trim, the X has a very vulnerable oil pan coupled with a good AA. So you can actually clear a rock with the bumper only to hit it with the oil pan, especially if descending a rocky hill. Ouch. This won't happen on a Subaru. Conversely, what drives me nuts about my front skid plate is that it has a low sitting edge right in front of the front wheels. So I was hitting that all the time before the lift. Had the edge been behind the edge of the tires, this would not have been an issue (may be impossible due to the exhaust tubes).
Clearance G: Footprint and Wheelbase
Wheelbase: see above, plus turning radius. But overall footprint, too, matters a great deal on tight trails. It also allows Samurais and old Foresters to go around stuff that others must negotiate. The disadvantage of small vehicles is on steep terrain with big ledges, but no street-drivable Subaru deals with big ledges.
Clearance H: Water fording ability
High-end off-roaders have 30" and up out of the factory.
There is a thread about Subarus here.
Beyond traction and clearance:
1. Reliability.
2. Weight.
3. Rollover angle. Hey, one thing I am not losing much sleep about!
