The United States does not really have the kind of old class-conscious culture that makes regional dialects more or less dignified to the extent that say European countries or even England does.

Southern accents are typically a punching bag for comedians, because to most Americans they sound stupid. New York and Boston are perceived as sounding aggressive. Western and Midwestern accents are generally considered neutral, but in some places, especially California, people from outside the region might perceive a very hard elongated "R" sound.

One really major dialectical divide that pervades America is what could be described as African American Vernacular English. With the exception of the really "country" South, Black people from cities all over America sound remarkably similar independent of geography. There are historical and culture reasons for this.

The closest thing I can think of that is very explicitly "dignified" is that there used to be something called the "Transatlantic" accent, that was sort of a phony pretentious half-British American accent. It doesn't really exist anymore in any notable way, except maybe some holdouts in snobby rich families in the mid-Atlantic, but a good example is how old time movie actors from say the 40's and 50's talked. A very specific example from fiction is the character of Thurston Howell on the old television show Gilligan's Island, and a real life example is the late William F. Buckley the political commentator / pundit / author.