Personally I like facebook the most out of all of those three. Mainly because people don't and can't use html on their profile. Which gets rid of those annoying graphics and stuff that people use on their profile. It also get's rid of all of those stupid spammers that are on myspace. So basically I like he simplicity of facebook. There's only one thing that I would change, that face that people can see everytime people write on your wall. That gets kinda annoying.
Yes, but there are already hundreds, if not thousands of social networks out there. Advertising will help you out a lot. Unless you already have a bigger site that you can promote on. Plus just getting programmers to program it is going to put a big hole in your pocket, that is if your network is going to have all of the features that the others have and more.
MySpace target audience is young, adult males with acne, glasses, that are dressed in all black, and on the verge of committing suicide. It is not for me, therefore, I don't like it.
I hate MySpace. Too many people spamming on there. Soon they will be selling cocain, and other forms of drugs. Maybe Viagra? Or they might be on there already.
I have to say I am still impressed by all three sites, though I only peruse MySpace and Facebook habitually. Can't consider any of them worst, but I chose Bebo as I just don't use it. Which I suppose makes it suck.