Since I have noticed comments about Twain's "slow" way of speaking, I
have always assumed that he would have had more of a Southern accent
than most people in the Hannibal, Mo. area would have had. His
parents, after all, were from Southern states before they moved and
would have brought their speech patterns with them. Little Sammy would
have developed his speech at home, influenced by their way of speaking,
no doubt.
In his public speaking, I believe he would emphasize his "drawl" for
comic effect. To my ear, the recording of Wm. Gillette's imitation of
his friend and neighbor Mark Twain's speech bears this out.
Jerry Dean