Disrespective:
The Mazda 6 is also decent but arguably not as good as the Subaru. Both would be very competent so will test drive them with the whole family buckled in to confirm space.
Keep an ear out for road noise in the mazda. For a start, they are a lot louder when you only have 2 up the front, or driving alone. Ours is shocking on brand new pirelli tyres.
And make sure to hit some bumps and see how the steering responds. We took ours 500k on a holiday and I was tired from fighting the wheel to stay in our lane at 110kph, when a 500k trip used to be half a days work in a semi.
We're both pretty disappointed in the Mazda 6 wagon and are thinking about selling to buy another BMW (5 -series wagon) just so long trips are comfy. I think they're fine for around town, but way too hard in the suspension for Aussie roads on long trips.
Disrespective:
In an ideal world we'd get the BMW and not expect reliability issues but i'm wary of maintenance costs on them...
Find a good independant BMW mechanic and you'll be laughing.