Figuring out who's point of view your story should be in is essential to it's success. My first book had six main character, oh yes, six. I loved them all and thought each one of them was strong enough to be the story's protagonist. However, I made the mistake of not picking one and wrote it from an observer's point of view. I even made the horrible mistake of occasionally jumped into different characters heads, without a change of chapter or a break. You can imagine how incredibly hard this was to read. Hey, when I make a mistake, I go all out.
That's not to say this kind of thing can't be done. However, you must be an experienced writer to pull it off and 99% of the time, if it's your first book it won't get picked up if it's written that way. This is often seen as an amateur mistake and agents and editors will usually pass on a book written like this.
So I had to fix my book. The really hard part was deciding who's story it was going to be. I loved all six of them and thought they all would make a great protagonist. But I had to pick. So I looked hard at the plot line and saw whose story had the most ties into it. Once I did that he jumped right out at me, practically smacking me upside the head. It was that obvious. The other characters are all still integral to the story and are strong characters in their own right, with whom I could easily do an offshoot novel. However, they will have to wait for their time in the lime light. By the way, I don't recommend having six strong characters with integral parts in the plot, it is a lot of work! I can't wait to write a book with just one or two!
Here are some great links on the subject: