Hi lfender,
As a basic CD/data back-up burner for the 788, either one does the job; I have the CD-R one, which is discontinued.
Of course, with the CD-RW one, you get the option of using CD-RW discs that are re-writable, thus the possibility of keeping your 'coaster count' down by doing rough evaluation mixes, erasing the disc and using it again.
Best,
CC