Has anyone done the Milford Sound cruise with Mitre Peak Cruises? If so, were you satisfied?

Mitre Peaks seem to use smaller boats than Realjourneys and Red Boat and that appeals to me as, being closer to the water, one is likely to see more waterlife (dolphins, seals, penguins, etc). However, their nature cruise is shorter than the others (2hrs, as opposed to 2:15 for Red Boat and 2:30 for Realjourneys) so I'm wondering whether a) they go faster b) they miss out some places or c) both.

Comments on any of these companies/cruises would be helpful. Thanks.

Therer's not much to choose between any of the cruise companies in Milford. Whichever you choose you will have a great trip. There's been a lot of discussion about small boats v's large boats, and frankly none of them hold much water (pardon the pun) IMO a small boat full of people is more crowded than a large boat full of people, but some folk instincively prefer one over the other, and that's fine.
You will see the same wildlife regardless of which boat you choose. The seals and possibly penguins will mostly be on the rocks, and you will get within about 20 meters of them. The dolphins will probably be surfing on the bow wave, so you will need to crowd on the bow to see and photograph them.
As to the different cruise times. This has more to do with what time they have to get back for the next cruise, rather than speed difference. Obviously the boats do differ in speed, but they never operate at maximum speed anyway, so there is always reserve. You will see the same things regardless of the cruise you choose. As a comparison, the scenic cruises cover the same ground as the nature cruises, and they take 1hr 45 min. The nature cruises just spend more time mucking around.

vbca is right. It doesn't make much difference. The boats follow one another up one side of the fijord and back down the other. They all stop in the same areas to view the different wildlife, waterfalls, glaciers, etc. The boats are evenly spaced out around the fijord so there's never a feeling of being crowded. Regardless of which boat you choose it is a fantastic not-to-be-missed trip. It was one of the highlights of our trip to NZ.

Thank you both for your very knowledgable and informative responses. I have booked with Mitre Peak Cruises and have tacked on the underwater observation thing. I wasn't going to do it, but I have read many reports from people saying that they enjoyed it so, since I'm probably only going to be there once, I might as well do it all ;-)

The "underwater observation thing" was pretty cool. I thought it was worth the extra time. By doing that we also headed back to the dock on a smaller launch and were follwed by a pod of dolphins.