A little late to this post, but my favorite cruise lines would be Princess, Holland America and NCL.
I've cruised one time each with Princess, Hal, Carnival, Disney, Royal Caribbean and NCL America. And I'm going back to Mexico with my partner on Princess in January. All cruise lines have their pluses and minuses, and I've never been on a cruise I didn't thoroughly enjoy. One of these days I want to try Celebrity - especially the incredible looking new Solstice!
My reason for selecting Princess, HAL and NCL is that they offer restaurant style seating in the dining rooms - meaning you aren't "forced" to have other tablemates. Typically, my partner and I sit at our own table at dinner, but often opt to sit with others at lunch as we do enjoy meeting other passengers. Most cruise passengers are fairly tolerant of lifstyles different than their own, but having the choice to move around each day takes the pressure off. i.e. no worries about bigoted tablemates.
Princess hosted an FOD reception on day two of the cruise, and went out of their way to ensure gay couples were treated well.
HAL hosted a lunch on the last day of the cruise. It would have been nice to have the FOD function earlier, but the fact that they popped for wine made for a very nice afternoon.
One of the most surprising times though was on HAL Pride of America. A young photographer asked if my partner and I wanted a photo taken of us holding hands! This was in the main lobby none the less. We must have looked extremely surprised as he then quietly verified that we were in fact partners and not just buddies.
In all fairness to the other cruise lines, we have never felt "lesser than" on any. Most employees are just grateful if you treat them decently. And most passengers are fairly well traveled and are used to a wide variety of people. In fact, our table mates on Royal Caribbean included a lesbian couple, a Mormon family with two VERY handsome college age boys, and a couple from Japan who spoke virtually no English. An odd mix, for sure, but everyone had a great time and we all returned to the table on subsequent evenings - so it couldn't have been too uncomfortable for anyone.
BUT, my personal preference is to have a choice on who I like to dine with.