The OBCR has the superior Ulla, and some nice bonus stuff like the Overture, the complete Along Came Bialy, Where Did We Go Right?
The soundtrack has the superior orchestrations, which are superior enough to warrant buying. Unfortunately, it has Uma Thurman and cuts made to the score. It has two useless new songs which don't really make up for the ones cut. But really, it's only just slightly less worthy than the cast recording.
I'd buy the OBCR now, and perhaps supplement it with some stuff from the soundtrack from iTunes if you feel inclined.
"...everyone finally shut up, and the audience could enjoy the beginning of the Anatevka Pogram in peace."