Stupid question, how was Twitter bad with external developers?
I've built a few services using Twitter, Facebook and Google+ each time and I didn't have anything bad to say about Twitter, they were always the easiest to deal with.
It wasn't with those things - that's what they want you to do.
It was appalling with developers of Twitter clients suddenly introducing harsher rate limiting, and a user cap per API key (meaning any growth in the app was severely limited, or even non-existent if already popular).
I've built a few services using Twitter, Facebook and Google+ each time and I didn't have anything bad to say about Twitter, they were always the easiest to deal with.