Which landslide was greater?

[Michael Z]

In terms of voting difference, or in terms of the effects it had? Well, in the latter case it's a tie between FDR '36 and Reagan '84. FDR's victory in 1936 sealed the New Deal and thus shaped American domestic policy for the next three decades. Reagan's victory in '84 marginalised the liberals and ensured until very, very recently that, if Democrats wanted to win an election they had to pose as a conservative (vis-a-vis Clinton, Gore, Kerry). So it's arguable that both victories had a significant impact on the wider historical- and sociopolitical spectrum.

Looking at LBJ's victory in 64, yes it helped cement the Civil Rights Act, but Goldwater's ideological legacy eventually led to Reaganism, and his candidacy as a whole ensured that the Republicans would be dominated by the arch-conservative wing of the Party for the foreseeable future. Equally, Nixon's 72 victory meant diddly squat when you consider that he resigned two years after and the Republicans were, for a short while at least, driven to the political margins because of Watergate.