Out of the available operators, we appreciated Mitre having a relatively smaller group, though the boat did get crowded when all passengers flocked to the same area. The boat was basic, but solid and clean. Although staff and service was at a good standard, you could barely hear the commentary during the trip. Basic tea and coffee included.
Overall however, considering the vistas of the Fiordland, probably 70-80% of the experience is the drive there and the view from the port, and 20-30% is the cruise itself. Milford Sound is surely worth a visit, but take a cruise only if you’re not on a budget.
Note: Regardless of the tour, expect (and prepare for) hordes of angry sandflies at the approach and the dock, but not during the cruise itself.