Seen both a few times, both also personal favs. Not really comparable IMHO. Zep has a wider range of musical style, Floyd undeniably produced the better psychedelic sound with a far superior technical edge. Nothing compares to the overall sensory experience of Floyd in concert. Zep was the forerunner and creator of the heavy metal sound.
BTW, if your knowlegde of them is limited to comparing Stairway and Numb as the best offerings of either of these groups you don't even need to be thinking of comparing them. Do yourself a favor and dig a little deeper into their libraries, then you will understand just how unique and different they really are from one another.
Also seen Rush and The Who along with many other all time classic bands. Fell asleep at AC/DC, even when they lifted two cannons out of the floor and fired volleys into the crowd lol. Being a Cleveland resident I was also fortunate enough to attend the Rock & Roll HOF concert, more legends performed than I can remember. Worked as a DJ and enjoy modern bands of most genres including rap but todays music is crap compared to the past.
The Beatles started out sounding just like every other top 40 band of the 60's, hardly innovative in the beginning. It wasn't until their exposure to the progressive American musical scene did they begin to experiment with their sound.
Oddly enough my long time sig here is the last few lines of one of my favorite Floyd songs.....