I'm using Ubuntu 18.04 and searching for a good file manager to replace Nautilus, based on the following criteria:

• Overall performance
  • Copying many small files needs to be fast
  • Searching files should be fast
  • Displaying many items needs to be fast, ideally with on-demand loading (Nautilus is quite bad at this point)
• Straightforward user interface
  • Basically like Nautilus' user interface before Ubuntu 18 and the switch to GNOME
  • Should not be too "laggy"