Actually a tie, but tilz LBJ. He got most PV votes, 61.1%. A record that will, I think, remain unmatched forever.
LBJ under-performed considering who Goldwater was, how he became President, and the nature of his campaign: I mean he really should have cracked 60% in California for crying out loud. He also should have been able to win Arizona, which still had a decent Democratic Party then.
So I'll go with FDR.
However, Franklin Pierce in 1852 is also worth a mention on that front.
With 50% of the vote? He got 85% of the electoral vote; something that FDR outperformed twice (1932 and 1936) and tied once; in 1940. And 1944 was just slightly less (81%). Pierce 1852 is very simular to Reagan 1980 in terms of PVs and EVs.