I have been with two volli houses and one used 1 1/2 and the one I am with now uses 1 3/4. Here is the discussion, do you fellow firefighters out there have a preference, and what does your house use?
An advantage of using the 38mm for wildfire work is it helps in water conservation. We use smaller capacilty branches (nozzles in North America) as well for wildfire as there's usually a fair drive to the nearest water supply - be it hydrant or static source. We have to be very careful how we use the wet stuff.
For structure fires we still find that the 38mm is a good size for most jobs. We train to put out the fires of course, but we also train to do it using minimum water. The thrust for that aspect, mimimising water damage to non fire affected property is possibly driven by the fact that most of my fire services money comes from the insurance companies. Whatever the reason, it works for us.