Gyokuyoutama

Bunny Must Die is more straightforward and shorter than Rabi Ribi, so if you don't want to be playing both at the same time you could play one and then the other.  In particular BMD has I believe 8 bosses in each of the two stories, where Rabi Ribi has like thirty or something, before you start in on the DLC.

There's no real direct link between them though so beyond that it doesn't matter (though Rabi Ribi's hardest difficulty originally was called "Bunny Must Die" rather than "Bunny Extinction").