My favorite is the 1938 version with Reginald Owen, Gene Lockhart, Kathleen Lockhart etc.
I think it is amazing because even in 1938 there were a lot of people who had first-hand recollections of Victorian England. Shoot, Gene and Kathleen Lockhart could have had personal memories of it as did Reginald Owen who was older than they were.
The 1951 version comes in second, but it isn't as faithful to the original story by changing ages around and adding characters.
(Of course the 1938 version leaves some of the parts of the story out too.)