Apple devices will always use AAC codec if I remember which is is not only compressed, but will also try to compress with lower bitrates than say a regular mp3 cbr compression by judging which parts of the audio signal can be compressed more heavily according to what we should be able to hear. I think apple devices do not support lossless bluetooth.
Android devices were known in the past to use a bitrate that is dependant on the amount of processing power the encoder gets assigned from the system. This means that on some phones with power management that is not designed with encoding for bluetooth in mind you would end up with horribly low bitrates because the power management would take away processing resources from the encoder to save battery. This of course would not apply to lossless codecs, if the sender and receiver support them both and the software picks it up correctly.