Here is my impression of "most well-known" for various US cities (including ones I've never lived in, where I probably have a more accurate perception
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NYC: Broadway, Park Ave, 5th Ave
LA: Wilshire or Hollywood
Chicago: Michigan Ave, LSD
SF: Market, Mission, Lombard, Van Ness
Boston: This one is tough. Maybe Fenway by absolute name recognition (but not because of the street, more of a coincidence). Maybe Beacon or Newbury or Mass Ave or Washington? Mass Ave is definitely the best known in Cambridge.
DC: Pennsyvlania Ave
Baltimore: Charles St?
Detroit: Woodward
New Orleans: Bourbon St, maybe also St. Charles Ave
Memphis: Beale St
Nashville: Broadway
Philadelphia: Market, Broad
Atlanta: Peachtree