Grant was close to the bottom in the first three Siena polls (1982, 1990, 1994), beating out just three presidents each time. In the 2002 edition, he moved up the 35th (of 42). Now, he's escaped the ranks of the failed presidents entirely, rising to a respectable 26th. This matches what other surveys have been showing. The very first such study, conducted in 1948 by Arthur Schlesinger, Sr., had Grant second-to-last, and up until recently he was invariably a bottom-five choice. Now, with Siena joining the crowd, he's a mid-pack president. Siena's respondents docked him for his executive appointments and executive ability, and didn't really give him strong marks anywhere, with it all averaging out to 26th place.
Next for me, I think, is David Herbert Donald's Lincoln, and then Jean Edward Smith's Grant.