Like Jim, I have a lot of catching up to do, but so far I have sailed on Princess (several), Norwegian and Windstar. I loved Windstar and if money were no object, I'd stick with them for all my cruises. Second place would be Princess.
The lines I'm hoping to try in the not too distant future are Celebrity, Renaissance and Royal Caribbean.
Norwegian is my least favorite, but I'd want to try them one more time before I write them off. I sailed on the line a few years ago when they were having significant financial difficulties and I hear they have steadily improved.