My husband and I took an Alaskan cruise last September. We did the Inside passage from Vancouver (cruise departed and returned to Vancouver). Our ports of call were Ketchikan, Juneau, Hubbard Glacier and Icy Strait Point. Since it was a loop, we didn't have to worry about the Inside passage vs. gulf side since you'd either get the views on the way out or back into port. I would highly recommend a balcony - we really enjoyed having breakfast and drinks out there (weather permitting).
I can't speak to Vancouver vs. Seattle, but we spent 3 days in Vancouver pre-cruise and LOVED it. It's a wonderful city, very clean and walking friendly. Lots of great restaurants. That said, Seattle is a little easier to get to and I know Southwest flies there, so it might be more economical. We flew to Vancouver on miles, so it wasn't really an issue, but I'd imagine it's more expensive.
We did a Celebrity cruise, which is a little more adult oriented and we cruised just after Labor Day, so there weren't as many kids. This was by design, since this was our last "adult vacation." However, we were told that the week before there were over 500 children on board, so I think Alaska is becoming more popular for families. I think Royal Caribbean and Princess are more family friendly and have better children's programs.
Other tips that we found helpful
1) Be prepared for the wet weather. We dressed in waterproof layers and it didn't affect our vacation at all, but there were passengers who clearly thought an Alaksan cruise = Caribbean cruise and were dressed inappropriately (shorts, sandals) and were pretty miserable.
2) Bring binoculars - I read this tip and thought it was silly, but there's so much wildlife (whales, eagles, porpoises, bears, seals) that you can see from the ship or on excursions and we ended up using them a lot.
3) Try and book your land excursions in advance through independent operators outside the cruiseline. We found the Alaskan message boards on Cruisecritic.com to be a great source for this. We ended up doing our own excursions that were a lot smaller than the ones offered by the cruise and I think we had a better experience.
4) We loved the Hubbard Glacier - that was one of the highlights of the cruise for us.
5) If you're prone to sea sickness, take Bonine (over the counter). I took one every day, starting from when we boarded and I never got sick, and I get sea sick very easily! We had one night where the seas were pretty rough - the dining room was about 1/3 empty - and I was fine.
Hope that helps - have a great cruise!
