The only people who would suggest that BJ Novak's best role was in Saving Mr. Banks would be people who have never seen any episode of the US version of The Office. The character of Ryan played to Novak's strengths perfectly, and also allowed Mindy Kaling and Stever Carell to expand their own characters on the show.
BJ Novak's best role was in Saving Mr. Banks. The historical setting suits his acting style very well. His portrayal of Robert B. Sherman alongside Jason Schwartzman as Richard M. Sherman is superbly executed. BJ Novaks is a great actor with a long list of films to his credit; Saving Mr. Banks was his best role.
It was the best of his career so far, but to be fair there really aren't enough roles of any size to compare it to. I enjoyed watching him as Robert Sherman, but I didn't think he stood out, really. I do think he has a lot of talent which will hopefully lead to more, larger roles in future, and then we'll really have something to compare this one to.
BJ Novak is best known for his role in the hit tv show "The Office" and this is the role that he has played the best. In Saving Mr. Banks, he is only a supporting role, and not the main character. "The Office" is a well known show that really is funny.