X1, hands down
1) There is no indication that a new 3-series wagon will be offered in 320d xDrive form. Although nothing has been announced, I would be surprised if they do, since that would be 4 powertrain alternatives rather than 2 or 3. (Note that past wagons sold about 1/2 xDrive, and only around 3K/year of both rwd/xDrive total).
2) I drove my E46 330xi on gravel/dirt roads. IMO it didn't provide enough clearance to do that except on roads that were graded/maintained (and with the federal budget the way it is, most are not). I definitely bottomed out, even with care in choosing the best path. You will be ok only on main USFS XX roads, but not on XXyy side roads.
3) There is not enough suspension travel in the wagon (sedan) variants to properly absorb many larger road features, even if you don't bottom.