Facebook app vs. standalone site?

So I’ve got this new idea for a little social web app, and I’m really excited about it because it’s in an area that I’m passionate about, it’s got lots of viral expansion possibilities, and it’s a pretty simple idea, at least in v1.0. Really simple. Like, knock it out in a weekend simple. So I’m going to try and move forward with it over the next few weeks, but I’m having trouble deciding whether I should launch a standalone site or a Facebook application first. My eventual goal would be to have the app as both a Facebook application and a standalone site, as well as iPhone, Android, OpenSocial, and wherever else it fits. But the question remains: which do I launch first?

Arguments in favor of a standalone site first:

  • More straightforward development process, whereas developing for Facebook is a pain
  • Platform isn’t changing while I’m working, unlike Facebook
  • I own my users
  • Integration with 3rd-party services feels more natural for some reason?
  • May be a better fit than the Facebook audience

Arguments in favor of a Facebook application first:

  • Faster development time
  • More social integration points, like News Feed, Notifications, etc
  • No competition at all on Facebook right now, unlike the web, which has one with a similar idea
  • Faster viral growth
  • Joyent’s free Facebook application hosting

I’m leaning towards Facebook at this point, but I would love to hear everyone’s thoughts on which approach I should take, and what other questions I should be asking. I’ll be sure and post my decision in the next couple weeks and I’ll be excited to hear what you all think of my little project. Thanks for your feedback below! (hint, hint 😉