For me, Led Zeppelin is the alpha and the omega and has been since I was about 8-9 years old, and as weird as it may be, I considered that when I were to die and go to heaven, and were given the choice of two bands to whom I could listen for eternity, they'd be Led Zep, and Steely Dan, but some years later it occurred to me that were I allowed a thord, it would be DP. Their Mk II lineup and output was stellar. I saw them twice, and Rainbow one or two times back in the late 70's-early 80's
Sabbath isn't even in the same league, although I was into them for about 15 minutes when I was 12-13. Not that they're bad, but as a friend once described, they're just missing that unquantifiable "something." Maybe it's that they are a bit more simplistic, or as an above commenter said "riff based," but even though I really like some of their Dio stuff, and Paranoid was an important album, they really don't make the cut.
Simple, straight ahead R&R can work (see AC/DC) but there's just something about Sabbath which rubs me the wrong way (pretence, mebbe)