Welcome to cruise-chat.
It is really not possible to simply say one line is better than another when discussing the major cruise lines. What I like may not be what you like. Thus if I tell you to go with Holland America and you don't like their product, you'll think I'm an idiot. Picking a good cruise usually has to do with your likes and dislikes and what you like to do. Holland America, for example, normally has an older clientele although younger people cruise with them all the time. They are a more sedate cruise line as compared to Carnival, NCL, and to a certain extent Royal Caribbean where there is more nightlife and excitement.
I'm afraid you won't find king crab legs and lobster in abundance on any mainstream cruise line. Most cruises offer small lobster tails on one night during a 7-night cruise. I've not seen king crab legs offered although I guess they can be found on premium lines or in the extra-fee specialty restaurants on some ships. Those old TV images of Love Boat waiters parading into the dining room with huge platters of lobster just don't happen. Food is just as subjective as picking a cruise line. Celebrity usually gets the nod for having the best of the mainstream lines, but personally I think they've gone downhill over the past few years.
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Booking tours for an Alaskan cruise can safely be done on-line with private tour companies in the various ports. They will be cheaper than the ship's tours. I normally recommend buying ship's tours for first time cruisers, but Alaska is an exception since it is a state and the tour operators are quite reliable and extremely competent.
If your cruise goes to Skagway you MUST do one of the train excursions. Breathtaking scenery. Doing the dog mushing on top of a glacier is superior to going to the dog sled camp in Juneau, where the dogs pull you around in a wheeled cart.
Cabins are pretty much the same from line to line as far as what they have in them, unless you go to suites.