I can't really speak for the ships but the differences in the cruise lines. Our first cruise was a carnival and we had nothing to compare it to, next was a royal caribbean and honestly we couldn't tell the difference. So we took another carnival and very quickly could see the difference and realized we were on our last carnival. We went on the Dream and it was there newest and biggest ship at the time. The ship was less than 4 months old, the kids liked the slide but even they prefer royal caribbean. The best way I can describe it is: it is like comparing a brand new motel 6 to a Marriott. Although there is nothing wrong with a Brand new motel 6, I wouldn't pick it over a nicer hotel even if the hotel was older. Something to think about also is that Vision was just redone this last year.