I'd have thought surely by needing a 4x4 you'd rather the torque of the diesel?
Not to mention that the diesel also makes more power (granted the petrol is a whole 0.3s quicker to 62).
I'd take S-Tronic over manual though.
I've been looking into these as the parents have expressed a interest in one. So looking at the various options for them and ill give them a list.
Id agree with the S-Tronic gearbox option.