I took several glacier tours in June 2008 from Whittier, Seward and Valdez and they were all good. So if you have to pick one, don't worry too much and take the one most convenient to you/your itinerary.

What you really need is good weather i.e. no rain. This is something no tour company can control.

I took Prince William Sound Glacier Tour from Whittier before my cruise departure in the evening. I also bought their motorcoach transportation from Anchorage which is also cheaper than the cruise company's bus from Anchorage. The tour company's bus picked me at my hotel in Anchorage. It was a proper motorcoach and not a small shuttle so they also stored my bags properly in the coach. The coach dropped me off at the tour boat dock (bags stayed locked in the coach the whole day) and after the tour the same coach dropped me and my bags at the cruise ship check-in in Whittier.

The tour itself was very nice and showed us up-close view (within 250 feet) of Surprise Glacier. Other than salmon, otters and birds you don't see any other wildlife in this part of the sound.

The tour also serves free lunch including a nice vegetarian lunch. Free coffee is also available the whole day. Other snacks and beverages are available for purchase at very reasonable prices (like 1.00 or 2.00 USD). No rip-off at all.

The difference between Prince William Sound tour and 26 Glacier tour is the first one shows you 1-2 glaciers and wildlife up-close and peacefully, will stay close to the galcier for 30 minutes allowing everyone to take enough pictures. The second one shows you only glaciers (no wildlife) spending only a few minutes at each. It does show you 26 but most of them are at the top of mountains, up-close are only 3-4.

Overall a very positive experience.