Imho, there is an important technical side to this discussion. How scalable is your application? A bunch of friends scalable is a far cry from TechCrunch scalable. Are you confident that if you break on TechCrunch, your app won't fail? There's nothing worse than breaking big and then... breaking big. People will lose all faith in you. If your site is ready technically, why not just put it out there? There are probably way more potential compteitors here, so in some sense you are launching to an unusual pool.

On the other hand side, if your application is not yet scalable - private or invite only beta is probably your only option.