But you didn't express it as your personal opinion. You said "the usual top five list" as if it were some objective list written in stone, not "my usual top five list", or "my usual top five list based only on dive ops that I've personally experienced". No, you don't have to dive with each of the dive ops on your list multiple times to say they're the best, but you should dive with all the other dive ops on the island before making that kind of judgment call. Otherwise, they're only the best dive ops whom you've actually dove with (and in your personal opinion, based on your personal qualifications), not "the best" period.