Sox
Avoiding The Swan Song
Both bands are in my top list of all time and along with Sabbath they initially helped shape the British Heavy rock scene. I have gone with Zep at their zenith but it's a mighty close call.
I only like some of the songs of both bands. I am picky and selective. I like the best songs of Deep Purple even more than I like the best songs of Led Zeppelin.
But *Blue Öyster Cult* are the kings of heavy metal/hard rock!
Nothing by Deep Purple or Led Zepp beats Tyranny and Mutation and Secret Treaties!