Have used 25mm, 38 and 64 at structure fires - each has it's own application.
25mm when backed by a good pump (aka not one of the old 24 or 34 types) works well in a going structure, for direct attack only. easy to move through a house, and quick - no good however from a well involved area if you intend to minimise damage by gas cooling, however very effective for painting, penciling and direct attack to fire seat.
38mm is my weapon of choice for a going incident, great for knock down, great for gas cooling, penciling and painting and not to cumbersome to more through a domestic structure.
64mm - suround and drown people, this ones a car park - some services use this as their primary hose, as their main methoid is surround and drown. Good for large incidents, to commence the initial knock down to allow possible entry - near impossible though to use inside