The verdict - EmelFM2 - 8/10
Orthodox file managers have been around forever, and have evolved from simple CLI-only utilities for moving and renaming files to comprehensive file commandeering tools that'll give many modern GUI file managers a run for their money.
The top two contenders reflect this transition, but ironically neither carries the trademark 'Commander' moniker. At the expense of being krucified by the Krusader users, we'll offer the top spot to EmelFM2.
Feature-for-feature you can do more with Krusader, but a fully-loaded app isn't always the best. Krusader is deeply integrated into KDE, which is good for KDE users, but what about the rest?
On the other hand, EmelFM2 just needs GTK, and works well both in Gnome and KDE. The biggest issue with EmelFM2 is that it doesn't have a virtual filesystem to connect to Samba and NFS shares, but on the bright side this helps keep the dependency list to a minimum.
Midnight Commander is like Slackware – you don't recommend it to new users, and those that are using it, would never use anything else.
Gnome Commander is a good option for Gnome users, but it relies on a deprecated piece of technology. The Gnome Commander developers also have a few plumbing issues to fix in their documentation and offer more control to keyboardies. If you are using Gnome (or not) and need to rename lots of files borrowing data from their metadata, there's no better way to go about it than with Gnome Commander.
Then there's Beesoft Commander, which is light in both size and features. If it does everything you need to do, you aren't doing enough!
Finally we have MuCommander, which relies on Java for cross-platform support and runs on Linux, Mac, and Windows, and even your web browser. It's a good tool for new Linux arrivals, but it lacks documentation, and forces users to modify XML files to edit keyboard bindings and change menus. What's going on here?
So there you have it. KDE-only users should use Krusader. If you hop distros, or don't really care which desktop you use, go for EmelFM2.