CASampledSP is a JNI-based service provider for the javax.sound.sampled.spi interfaces. As such it is capable of decoding many popular audio formats (like mp3 and aac) at native speed taking advantage of Apple's CoreAudio library. The focus is currently on decoding and converting to LPCM, not on writing or exporting.
FFSampledSP is a free implementation of the javax.sound.sampled.spi interfaces. It is part of the SampledSP collection of javax.sound.sampled libraries. Its main purpose is to decode audio from various formats at high speed using FFmpeg. To do so, it uses the tagtraum FFmpeg package, which offers FFmpeg binaries configured to decode audio while avoiding CODECs with patent problems. In other words, it supports formats like Ogg and FLAC well, while leaving MPEG-4 and MP3 unsupported.