I have been on both a Royal Caribbean cruise and two Carnival cruises.
Based on my cruising experience, (which is probably much less than some other members here), I found that Royal Caribbean and Carnival were about equal in quality.
I did like the food a little better on Carnival than Royal Caribbean. It seemed that the food seemed fresher and had a better presentation on Carnival. During my cruises I ate only in the main dinning rooms. So, I can't speak for the quality of food in the alternative dinning places on the ships. Some ships have upscale 5 star restaurants onboard.
Royal Caribbean seems to have the largest and most modern cruise ships.
A third choice in cruiselines might be Princess. I heard good things about Princess. I also heard that many middle-age professionals liked Princess.
I have never been on a Northern/Alaska glacier cruise, so I can not help you with that. I heard that these cruises may only operate during short time during each year, when the weather and temperatures are most ideal.
On both cruise lines, I encountered allot of crewmembers that were from India. Especially in the dinning room. On all three cruises I was on, the top waiters or Maitre'Ds were all from India.