Which was Led Zeppelin's best era: 1968-1973, 1973-1975, or 1975-1979?

1968-1973 is my favorite. Led Zeppelin I - my favorite album. Led Zeppelin II - fantastic riffs, Led Zeppelin III - way underrated, this one is great to, Led Zeppelin IV - some of their most famous songs. Also live this was their best period in my opinion; Page's solos were longer and more bluesy in this period plus Bonham's drumming was the most creative at this point.