That actually varies as well. Typically one would expect the USC line to always go much faster, and it usually does, but sometime a flight is just full of USC/PR passangers and not many visitors, so you get the opposite effect (happened to me twice).
Also now they fingerprint and photograph permanent residents. So what used to be "Hello!" + 2 questions now is "Hello!" + 5 questions + fingerprinting + photographing.
