I've done 2 Alaska cruises vs many Caribbean/Mexico cruises. I'd pick Alaska first (if I could afford it) anytime. I live in So. Calif and the scenery in Alaska is so different, so huge, I don't miss the sun at all. Also love to lie in sun around the pool, but first choice would be to sit on my balcony and watch the scenery/wild life in Alaska! Just a personal preference. Be aware that the airfare to Alaska is high and really adds to the cost of the cruise. Have fun choosing!
My husband and I have done 5 cruises, 4 to the Carribean and 1 to Alaska. Alaska has a lot of offer but the weather can make a big difference. We hit a really good week and enjoyed the side trips. Try out the Jeep /canoe excursion and the wildlife excursion. The narrow guage train ride is also worth the price as you get the best view of the scenery. If you something really challenging, hike the Chilicoot trail and then cruise!
My favourite Carribean trips were the "Saint" tour, doing St. Maarten, St. Thomas, St. Barts etc. I also really enjoyed our last cruise to Belize, Costa Rica and Panama. I would avoid the Mexico, Jamaica stops but did enjoy Grand Cayman.
We are sailing on the Conquest next May. This wiil be our 3rd Carribean cruise (1st Western). We went to Alaska in May 2003 and I had plenty of Sun. We only had about 3 hours of darkness. You will never see scenary anywhere to match Alaska. We got a balcony cabin (a must) and made sure it was on the side to see the coast line since you travel so close to it most of the time. The balcony also made a huge difference when we were going thru glacier park (because it was so cold and wet). The only bad part, as least for me, would be the cold. I couldn't really spend any time outside. We went on the Dawn Princess and it was a great trip.