Facebook Connect versus Facebook app?

Is it more useful to have a Facebook canvas app than simply having Facebook connect on your own site? Why?

As far as I can see, either one let's you get approximately the same thing into a Facebook user's stream, which is the only visible part to me.

Having developed both, I can say that developing a Facebook connect application gives you more control. If you don't need to show information on people's profiles (boxes) and you really just want to publish feed items - FB Connect is a simple solution. You can do other cool things like see what friends you have on FB are using your application, etc. It's a great way to see the effectiveness of FB marketing on your application as well. The number of FB Connected users is generally a good indicator of conversion from Facebook related materials.

Going with a canvas app does increase project risk, in my opinion. The platform is fairly young, and FB often changes things without prejudice. FB Connect is still subject to this risk, but I think it's less significant, and they generally seem to be a bit more caring when it comes to making changes on that side of things.

Oh, and use the JavaScript api instead of their FBML if you can help it - the markup it generates isn't standards compliant and can mess rendering up a bit.

I pondered this question myself at the beginning of the project I'm working on, and chose to go with Facebook Connect for my main site, but also develop a canvas app as a "lite" version. The reason were:

1. I was able to maintain autonomy with my site as far as UI and flow while still benefitting from using Facebook's powerful platform features. I can drive traffic to my fully featured Connect site using a smaller canvas version that exposes 1 or 2 features.
2. I would eventually like to consume competiting authentication providers, APIs, etc and not tie myself to Facebook. In 3 years time there could be a mass exodus of FB like we are seeing with MySpace now.
3. Facebook itself is promoting Connect over canvas applications. Furthermore, by going Connect I can further insulate myself from risk that another FB platform change can break my app.

I think it's about how you want visitors to enter your site/app.

Are the visitors already on your site? Use Connect.

Are the visitors coming from Facebook? Use a canvas app.

You could build both interfaces and share the business logic between them.