Of your ports, we went to Bergen, Alesund, and Olden. This was on Celebrity a couple of years ago.
Bergen and Alesund are done easily on your own. We did a shore excursion in Alesund, though, and it was good, yet next time we will opt for the tourist bus that goes around town. I forget if it was a HOHO. As you'll be going to Stavanger, you can do a fjord excursion from there and enjoy Alesund. Pretty architecture.
In Bergen, we walked into town and visited the Fish Market and Mt. Floyen. The tram up there was worth it. There were six ships in town the day we visited, so the wait was long, yet the view from the top is superb. You can hike to the top, if you wish. The paths are pretty.
Olden is a port in which you should book a shore excursion as there's not much to the town. Yet, the surrounding area is beautiful. We took a boat ride on Lake Loen with stops at one of the glaciers. It's among my favorite shore excursions ever.