Interesting..., and very much dependent on which boat you're on, I guess. Lots of people find the Bluebridge boats more stable. I quite enjoy the Bluebridge ones, and have found the opposite regarding the food :-), especially when it comes to breakfast.
Lots of personal preferences, I guess!
Yes, no doubt! And the weather. We got relatively smooth seas each time. I don't know which Bluebridge boat we got, but I think our Interislander was the Aratere...whichever is their oldest one. I like that the website shows you the difference between each boat.