My wife's preferred cruise line is Celebrity, mine is Viking.
Comparing Celebrity suite's class (Retreat) to a Penthouse Veranda in Viking, there isn't much difference in cost.
The food is much better on Viking. Service in the Celebrity Retreat class is a little better than Viking but not much. I prefer the atmosphere of Viking, relaxed, nice people.
I like sea days, long cruises and feel very comfortable on Viking. My wife likes the shows and other activities on Celebrity. For shorter cruises, we pick Celebrity, for long cruises, it's Viking.