The itinerary and dates have a great deal to do with the passenger mix you'll find. On Silversea last December, the cruise segment right before Christmas was lively and fun. The segment over Christmas and NewYear's Eve was filled with many folk who had nowhere else to go, and was generally dull and stuffy. Same ship, similar itinerary, but the dates were the difference.
I have also noticed a "Yellowstone Effect" in the lounges on luxury lines. If the lounge is empty, people just pass by when they look in. But if there is someone there, then other people will stay when they poke their head in. So, be the first to start the trend.
Luxury lines also tend to be more of a "cocktails before dinner" style than a "have a drink after the evening show" atmosphere. So meet fellow guests before dinner, then make arrangements to meet after the show later in the cruise.
IMO, all ships have their own personalities, even within a cruise line. The Crystal ships have different "feels", as do ships with Silversea and Radisson. But the good news is that you'll have a great time finding out which one's are best for you.