[ceejayoz]

That's a broad question without one single answer.

In my experience, getting approved to use the API is substantially easier with Facebook than Twitter. Twitter will reject for bullshit reasons, and send you a "there can be no appeal" message. The only way around it is to kick up enough of a fuss with prominent people to get a manual reconsideration.

Once you're in, though, you can pretty much do anything a Twitter user can do. Facebook heavily limits what data you can get - you basically can't get any info about the user's personal profile/feed, or info about a user's friends. Twitter makes all that readily available.

On the other hand, analytics.twitter.com has no API (and hasn't for years), whereas Facebook makes all sorts of analytics info available on Pages.

[paulgb]

One thing conspicuously missing is getting all of the replies to a given tweet. This makes it difficult to build anything resembling an alternative Twitter UI (such as existed the the hayday of more open Twitter APIs) using the official API.