balanced is preferred, lurkette summed it up very well i think.
but if i had to choose one or the other, i'd also go with interesting. i'm boring (to myself), if i found myself really interesting i wouldn't feel much need to talk to anyone else
that said though, the conversation isn't interesting if it becomes completely one sided. i can listen to an interesting person a long time, but eventually i'm going to want to input some of my own thoughts and opinions. if they won't let me do that, they'll cease to be interesting and just be annoying. interested works the same way though--how long could i stay interested in a conversation by myself?