Hello Lee,
PCM1802 offers 105dB Dynamic Range with -96dB THD
PCM1803 offers 103dB Dynamic Range with -95dB THD
PCM1802 also includes the analog anti aliasing filter down to 300kHz, which is a significant advantage. (and is costly to add in silicon). The PCM1803 relies on a higher frequency anti aliasing circuit internally (therefor smaller), and the user should add an external filter.
Is that enough to get started?