Which Facebook like button should I have?

I have 3 options for having the like button:

1. My Facebook App
2. My domain URL running the app
3. Fan page

I am more inclined towards using #2 as it will post a thumbnail on the user's wall and help promotion. What do I miss in #1? #3 looks very useless to me at the moment as fanpage is just a placeholder as of now.

Should I use one or two? And how much #1 is important for an 开发者_运维技巧app which is going to be viral?

Your question is not clear enough, but I'll try to give you a summary:

1. If your items (pages) that will have a Like button are accessible through an external website (e.g. a blog post) then go for option 2
2. If these items will only be accessible through the Facebook app (or meant to be accessible mainly through the app), then go for option 1. This way, if you had to move the site to another domian..etc you don't have to worry about losing the "likes" (because the links that being liked will be something like: http://apps.facebook.com/my_app/item/5 and won't get affected)
3. In my opinion, you should always have a Like button for your "brand" fan page (option 3) somewhere in your app!