This is an interesting thread, but needs more specifics. We all use one or more of these tools. Let's use our personal experience to be more specific.
Here are some random specifics. I'll add more in the future.
If you want syntax highlighting in TC, install one of the several available syntax highlighting editor plugins available. I use the hpg_ed plug-in, but SynPlus is also popular.
If you need virtual/temp folders/collections, try SpeedCommander. Its tabbed interface supports both "real" folder tab groups and virtual folder tab groups. IMHO SC's implementation is more intuitive to use than Dopus' or TC's, though it doesn't allow you to build subfolders in a virtual tab. Dopus does. TC supports virtual folders via file system plugins... there are at least 3 different implementations of TC plugins that support virtual folder hierarchies.
TC's Content plugins. The word "Content" gets bandied about. One of its meanings is "custom columns" in the detailed view of the file panel. The number of custom column ("Content") plugins available is staggering. You can have any media value extracted. You can show NTFS stream values. You can calculate various things. There is a Content plug-in that lets you specify what goes in a column based on filetype (like showing #files/#subfolders" in a column for folders and image dimension for jpegs IN THE SAME COLUMN). You can format dates, enter whatever text you want etc etc. You can use any value from a Content plug-in as a line of info underneath a thumbnail, or as a value in the renamer tool, or as a filter value, or in the "change file attributes" dialog (including saving to NTFS streams). This "Total" integration with custom metadata is unique to TC. Many other tools support a large number of "custom" columns, but mostly those are limited to what is provided by Explorer. Dopus, for instance. But no tool in my experience has the metadata content integrated into the software at such a low level as does TC.
Dopus, TC, and SpeedCommander (SC) support custom menus. TC via ini-like MNU files, Dopus and SpeedCommander via dedicated editors.
Salamander's toolbars are also customizable using a very cool editor.
TC has only 1 toolbar. It wraps if the window isn't wide enough. Antiquated. On the other hand, TC supports building the toolbar (as well as executing functions on dragged files) by dragging and dropping from the file panel. Brilliant!
Dopus and Salamander support central (vertical, between panes) tool bars. FreeCommander has a context-specific version of the same which has functions that switch context based on which file panel is active (ie move, copy).
SC has the best (most complete, easy to use, customizable) implementation of layout management, followed by FreeCommander and Dopus. Unfortunately Dopus does not allow "fixing" panel dividers (they squirm around a lot) which I dislike. It also has no internal commands to set the divider position (like 50%). Nor does TC (use the context menu on the splitter, instead), though TC WILL remember and restore positions.
TC 7 supports a single tree (a la Xplorer2... ) but also dual trees. But there is no way in TC to show a tree only in the right panel. Brain dead. Furthermore, the TC trees do not fully support drag and drop, folder renaming, or deleting. More brain dead.
SC and FreeCommander subordinate folder tree visibility to the active folder tab. You can set up folder tabs that have trees and others than don't. Wonderful. Dopus subordinates folder trees to the panel, so switching into another folder tab can't change the tree visibility (unless you explicitly script it). You can toggle each tree on and off, though. TC subordinates its folder trees to the main window, so you get either one (on the left) or two (both sides) and that's it.
SC offers a dropdown menu in quickview mode to easily select another view plug-in. In TC you have to highlight the panel and press "4" to cycle through viewers.
Salamander does not support quickview (ie preview embedded in the opposite panel) but instead pops up a new window. The window is very full featured, though, with menus, toolbar, etc.
Salamander supports individual "panel" toolbars which are customizable, a great feature.
Dopus is the only file manager I know of that attempts to emulate Vista's "breadcrumbs" bar. IMHO they didn't do a very good job (it's a separate toolbar instead of being integrated into each panel's path box). The SpeedCommander blog suggests breadcrumbs will be supported in SC v12. The preview screen shot looks superior to Dopus' implementation.
In my experience, Salamander ties with TC for the most crash-proof. It is also the fastest for accessing Network shares and in the responsiveness of the interface. TC is about the worst when accessing Network shares. In my experience. It tends to "hang" in situations where its competitors have already produced a dialog box.
IMHO Salamander is very good looking (nicely designed monochrome icons that show color when moused over, for instance) and has many "little" features lacking in the others. No folder tabs, though. No folder trees. No hierarchical favorites in Salamander, either. And only 10 "favorite" folders. Whuzzup w'dat? Salamander has great potential, though, and if you don't need tabs or trees or custom columns, really worth a look.
TC works great with AutoHotKey, but has no internal scripting support (only one command per button). SpeedCommander has built in scripting for buttons and menus using VBScript and exposes an apparently complete object model of itself. Dopus uses an internal scripting implementation which supports multiple lines of code per menu item or button, including prompts for parameters, but doesn't support conditional execution. Salamander's implementation is more like TC's... one line per button.
TC has the best "Overwrite/Replace" dialog of any of them. It shows these options: Overwrite, Overwrite all, Skip, Cancel, Overwrite all older, Skip all, Rename, Append, Compare, Rename existing target, Auto rename copied, Auto rename target, Overwrite all older and same age, Copy all larger/overwrite smaller, Copy all smaller/overwrite larger. That about covers it, don't you think? Also, besides the now ubiquitous thumbnails in the overwrite dialog, TC lets you specific as many meta-data values as you like (see above paragraph about TC's Content plugins).
I have bought/tried out/etc many file commanders (there are many not mentioned in the review at the beginning of this thread) but IMHO FreeCommander, TotalCommander, SpeedCommander, Salamander, and Dopus are the best of the breed, so they are the ones I know.
Who else has specifics?