Unity is the the user interface of Gnome. Nautilus is the file manager.
Unity is fairly slick but suffers a few issues – the main of which is when you’re doing certain thing I note little lags. Nothing major and not enough to deter me.
Now Nautilus – works well enough but if you’re doing copying over the net – don’t expect to use Nautlius for anything else.
I installed mc on the command line – probably use that for big file copying over the net. And in fact I’m pretty handy with mv, cp etc. at the command line. So perhaps I’ll use that a my default.
Or just ditch it all – install Kubuntu and be done with it, because I do find KDE vastly superior to Gnome.