Personally, I like the first four, for different reasons. One because it's so raw, with a teenage Robert Plant howling over the edgy bluesy metal that was to define the band's sound, Two because it starts using the studio tricks to enhance that sound, but retaining the blues bombast, Three because it departs and shows the bands softer side, and Four because it proves how much life there was still left in one of the greatest rock bands ever.
Depends what you want, Led Zepplin did some interesting and quite diverse stuff, for example, some of the later albums lean a lot towards folk whereas the earlier stuff tended to be more bluesy.
For my money, try Led Zepplin 1 and Led Zepplin 2 and see where it takes you.