As you know, I really don't have a loyalty requirement. My first choice is itinerary or ship. Like the Solstice was for the ship. I found that Celebrity was not my cup of tea. The upcoming cruise on the Epic was for the ship. I enjoy NCL and this will be my 5th cruise with them. The cruise in a couple of weeks was for the itinerary/cost. It's on Carnival, I've had 5 previous cruises with them.
I'm really missing Princess, though, so next year I'm going to need to go on Princess or Costa. Both of which I love. Princess is my favorite though.
So to answer your question, no, loyalty is not the main consideration for me.