I know this is an old thread (seven years!!!), but...
We've taken Holland America (1), Princess (1), and NCL (3). My first cruise was on Holland America's MS Amsterdam (not Neiuw) and it was great. This ship has been sold (now it's the MS Bolette with Fred Olsen Cruise Lines), but I loved it. Not huge, but a lovely ship...and it felt like an old time ship. My third cruise was on the Ruby Princess and we basically only went on that cruise because friends were going and invited us. For my second cruise we chose NCL because it was a great deal. It was a repositioning cruise that left from Vancouver and brought us home to Los Angeles (don't live there anymore). It seemed super convenient. Due to that cruise, we found out that NCL seems to have the best drink package, so we'll probably keep on taking NCL. Our fourth cruise (NCL) was Mediterranean and our Fifth cruise (NCL) was British Isles. All of the ships were wonderful. If I had more money, I would expand and try out some more, but as it is I'm happy to stick with NCL.