I don't really have an exact person for the "most interesting" as I talk to a lot of people who have their own individual style of knowing, participating and socializing in things. Everyone is unique in their own way as well so it's really hard for me to choose based on this.
I'd say some of my great friends that I enjoy talking to (and have talked to more than others) would be at the most interesting. I can't really judge others from who I haven't spoken to before as their posts can be one thing, but discussing an interest to an interest with them, another. When I say this I mean I might find one's post or the socializing with others pretty interesting, but after bringing up a discussion with that person myself, it could be a pretty different view.
So for my answer, it would be the friends I've been talking to a while now, and who's actually helped/guided me through things I needed help on. I find them the most interesting as they'll actually take time to say their wise words that I respect and appreciate very much. People like Signomi or Anastasia R., who have their hyper/silly times yet still know when and where to be mature and smart at are great people to meet and I'm glad to know them. I find people like this to be the most interesting for me. Of course there are other little details I find to call someone very interesting like their talent or their way of doing things, but this is just some things I like in a person to call them interesting. Many people are interesting based on what they do as well so I'd say several people come up as interesting. It's just I prefer to call one interesting from what I've known or know about a person and who I've talked to with myself as many times one can be very innocent to one person, but bitter to another. It all comes down to opinions on this though and I'd say more but I'm on my way to school I think I've summed up my main thoughts on interesting people. ^^;