In my opinion, I'd pick Celebrity or RCCI. I've been on all of those particular lines, hubby and I are I our 40's. We've done quite a lot of cruising and Celebrity was the nicest for us (did a transatlantic and a Christmas Caribbean cruise, both quite nice but completely different vibes). We have enjoyed our RCCI cruises as well, some more than others. The newer Carnival ships can be great but wouldn't recommend for a honeymoon necessarily. But, if they are in the mood to party down, then maybe consider it. Carnival has great entertainment. As for HAL, we sailed on HAL several years ago and it was just awful. the only saving grace was the excursions (we did a Southern Caribbean itinerary, our favorite) and at least we had that. The HAL cruise was not anything like we had hoped and we paid a huge penny for it. From food to the service, to fellow passengaram we just wished we would have booked a different line. I know it can be a hard decision finding the right one. Keep researching and think about what their criteria would be - accommodations, fancy food, entertainment, etc. I would suggest looking at Celebrity or RCCI for starters. We did our honeymoon on Adventure of the Seas. We absolutely loved it! Good luck!