Adam, it is true that the cheapest boats tend to attract backpackers and the most expensive boats tend to attract couples or at least dive buddies traveling together; that leaves the mid-range boats, which are a nice combo of both. They are not as posh as the high-end boats, but they are more comfortable than what bowmouth calls "bunk-aboards" since they have private heads for the cabins and semi-private rooms (some do have single rooms as well). These mid-range boats usually attract a slightly older average age group of divers--ones who can afford a bit more creature comfort and who often have their own dive equipment so are frequently on dedicated dive trips as opposed to backpackers who generally fold diving in as a part of a larger travel adventure. Mid-range boats do have some couples, but they also have lots of singles, so the social atmosphere is fairly inclusive. I would avoid boats in any price category that cater for one particular nationality, however, as if you don't speak that language it can get quite lonely!