I sail on NCL and have been really pleased with them. I sail solo as well as a 3 generation family, we all find our niche. Main Dining room meals are good, on occasion if I didn't like my first choice and made a swap, but that's probably been once or twice in 11 cruises. Solo meet up has been nightly and the host will even make a dinner reservation for the group so you can choose to do your own thing for dinner or join the group. I have cruise buddies from each of those experiences.
I recently sailed on Celebrity, lovely cabin but ship not as well kept, crew not as friendly as with NCL. Food was good, but I would give NCL the nod for both variety and quality in MDR and buffet. Only specialty meal was Sushi, outstanding food and experience. Overall I thought NCL had better entertainment, especially the musical talent. The string duo was different than I experienced on NCL and they were quite good. I also appreciated the Solarium: indoor and all adult was quite a treat!
I am looking for an Alaska cruise: RT Seattle so NCL is Bliss, Princess is Discovery and HAL is Westerdam or Eurodam, so quite a range. Probably targeting late May. Happy to listen to any advice on those three ships, timing, etc.