While both are outstanding with 3 well known singles each. As for the music, it probably simply comes down to personal taste.
In terms of sales, it's no contest. Led Zep the clear winner...by a long shot.
And then there's Stairway to Heaven! The most requested song on FM radio for a decade or more. Far and away the most sold sheet music every year.
Having said all this, Sympathy for the Devil is no slouch. I still listen to it today. "Ooo hoo, ooo hoo, oooo hoo!"
I agree with all you said except I think the Stones top Led Zeppelin in sales. Many, many more LP releases, and numerous charted singles going back to "Tell Me". BTW, if have any Stones vinyl LP's with a red/maroon London Records label in lieu of the blue label they are worth some bucks. There are two other Stones LP's that have nice value, the original 3D LP cover for, "Their Satantic Majesties Request", and the hexagon cut LP cover for their "Greatest Hits Vol. 2".