I know this is an old topic, but I still have a problem to find a good alternative, maybe I have high standards.
There is a 4 years old article about this.
But the question is, why is Nautilus so bad in two pane mode? Why is it so slow when browsing folders? And, why are all other file managers from article so ugly?
I like Krusader, but it does not looks near as good as Nautilus.
Is Nautilus slow because of the fancy GUI rendering? Is it hard to make file manager which fits nice in Unity?
What is your experience and what file manager are you using?
I got interesting results by making Krusader look native in Unity. I like it now.