I saw the Redford-Farrow film several times when I was young and it really defined the story for me.
The new DiCaprio-Mulligan version doesn't look as good to me.
Baz Luhrmann doesn't really do realism -- Moulin Rouge! definitely wasn't "about" the 1890s in any "realistic" way.
Also, when I saw the earlier version, I wasn't familiar with the actors as actors, so they could just "be" the characters of the story.
I'm pretty sure Sam Waterston is a better Nick than Tobey McGuire, though.
Have you seen the 1949 version I posted? It seems like most of the comments on this thread are about all the other versions. If Paramount later intended to keep the Alan Ladd version obscure in favor of the Robert Redford one, they’ve certainly succeeded.