We pick the line based upon a number of factors all related to the overall style of the line ... includes accommodations, service, food, and yes, a number of 'ambience factors'. That would include the dress code, lack of yapping on the PA system all day, and others that, for us, change whole the vibe of the onboard experience.
Then we work on itinerary. We need to enjoy the experience of 'getting there' as much as the 'there', especially on longer voyages.