Limiting it to 1932 through present, I'd say Wendell Wilkie for president (1940) and William Miller for vice president (1964).
Willkie stands out as the most formidable opponent FDR faced for re-election and him being the nominee as a businessman with no political pedigree was a big shift from the Republican orthodoxy (imagine Trump without the assholishness).
Want to argue Alf Landon, sure.
Yes, but Alf Landon was a politician (governor) left standing despite disastrous elections for the GOP in 1930, 1932, and 1934. There was also considerable excitement and some confidence from Republicans that he'd take out FDR (Literary Digest poll). And his loss is far more consequential and well remembered because the 1936 election is what sealed the FDR revolution, by the time 1940 and 1944 came around, from a policy change perspective it was much much less important that FDR win.
Landon also lived long enough (to 100) to become something of an elder statesman in Kansas. Ronald Reagan held an event celebrating him in the 1980s. And his daughter went on to become a prominent US Senator.