This is my opinion on Alaska...
The main thing is the itinerary and what you plan to do in port. Most itineraries are the same with the exception of which glacier you visit. I personally recommended Glacier Bay National Park for seeing the best glacier action. I have been on trips where we never even made it to the glacier to watch the calving because they path was blocked by chunks of ice.
When it comes to wildlife experiences, etc - plan to do them in the ports of call during "shore excursions" a big ship like Princess (or any big cruise line) is not going to stop just because it sights whales, but you can definitely SEE whales if you take a good shore excursion.
My favorite excursions have been whale-watching, visits to wildlife recovery centers, flight-seeing over glaciers and other such tours. I am just saying that I highly recommend planning for those tours before you pick a cruise - because you can arrange them before you arrive and make sure you get the best deals.
Juneau is great for whale watching and flight-seeing over a glacier. Sitka is great for wildlife recovery centers. Ketchikan is great if you want to take a nice long hike to a salmon rookery, following a stream of salmon swimming upstream.