Holland America has more experience with Alaska cruises than does Norwegian, but you should also note that HAL also has a different age demographic and tends to attract more older cruisers than does Norwegian. As far as drinking goes - the ships spend a lot of their time in Alaskan state waters which means they have to comply with state drinking laws. You don't see a lot of partying on Alaskan cruises no matter the cruise line you choose. For one thing the weather is so unpredictable that you won't see people laying around the open decks or around the pools. The southern area of Alaska is a rain forest, so it can rain every day for a little bit, or not at all. It can be 60 degrees one day, and 40 the next.
If you are 25 you might prefer the Norwegian Pearl over Oosterdam.