Based on my three stays at hostels in London, New York, and Chicago, I'm inclined to believe that there's a correlation between the quality of the rooms and the quality of the social interaction with the guests. The nicer the room, the less social interaction.
London: Camden Inn
From the pictures posted at their website, the Camden Inn looks like a bargain. Cheap, good-looking, clean rooms. Reality disagrees. The rooms are extremely small.
I stayed together with three other people at what would pass for the size of a bathroom in most hotels. The bed charged tossing and turning with metal squeaking so loud it wasn't even funny. The showers resembled vertical coffins more than places to take a bath. And from 8 am you could hear every single door slam as if it was your own.
But. The people I stayed with were really nice. There was the Danish couple from Aarhus and, of course, the lovely Julia from Lund, Sweden. The interaction was pleasant, polite, and even interesting. It was good.
New York: The Big Apple Hostel
The Big Apple Hostel had rooms at least twice the size of the Camden Inn fitted with the same number of people. The bathrooms were clean and suitable sized. The location perfect (two minutes from Times Square). Not having air condition (in 35 degree weather with close to 100% humidity) and no elevator (when you get a room at the sixth floor) dragged it down a bit, though.
Social interaction was markedly reduced, though. I had a chat with this rather cool Canadian punk rocker the first day, but that was pretty much it. And when the Italians moved in and started to use my towel, it kinda sucked.
Chicago: Hostel International
With four floors and room enough for five hundred guests, Hostel International Chicago was by far the largest, cleanest, and most professionally run hostel of the three. Every room had it's own bathroom and shower. Every bed had it's own power outlet. There was air conditioning. The beds was as squeaky as anywhere, though — it seems to be a hostel requirement.
But everyone was really, really old. It had anything but the feeling of a youth hostel, and the atmosphere showed it. Everyone went to bed early and rised equally so. Little to few words were exchanged with anyone. It had the personality of a hotel.
As a lone traveller, I'd take the Camden Inn over the Hostel International any day of the week. If I was going with someone else, I'd probably reverse my preference.