First, we never book excursions through the cruise lines; too expensive, too crowded, and too regimented. Most of the time we prefer to do our own thing and not book any excursions.
Among all the ones we have booked, I would have to say the most fun was the helicopter/dog sled excursion in Juneau, Alaska. That was amazing!
The most interesting would have to be our 2-day excursion in St. Petersburg, Russia. Now that was wonderful!
But the most awesome excursion was one we did on our own; we took the train from Katakolon, Greece up to Olympia. The ship's excursions were leaving late because the archeological site was closed until 2:00pm, but they didn't say why. When we got to Olympia, we found they were having the torch lighting ceremony for the Vancouver Winter Olympic Games! While we couldn't get into the site until 2:00pm, we got to watch the 90 minute ceremony on TV - it was fantastic. Then we watched the torch runner run out of the site with the flame and stop right in front of us to pass the flame to another runner. Then we got our picture taken with the first torch runner. To see the Olympic flame in person is awesome! But to see the Olympic flame in person with the first torch runner in Olympia was an amazing experience!!
Just can't buy excursions like that one!