Best luxury cruise line?

I suggest that you might find more of the information that you are looking for on some of the cruise related travel sites.
This link goes to a listing of 10 different boards.

https://blog.feedspot.com/cruise_forums/

I always am looking for the best value cruise, so I can't answer your question.

Perhaps that depends on one's personal preferences and priorities when it comes to amenities? You would be better served by looking at sites that focus on cruising. Cruise Critic website has a forum specifically for luxury cruises - https://boards.cruisecritic.com/forum/343-luxury-cruising/

Silversea
Regents
SeaBourn