It would be great to have comparing of two files feature some more specific. For example it could be nice to use tools like http://github.com/patraulea/LogDiff in comparing window or ignore characters seems like date/time while comparing of two logs. The usage could be like "F3" (list file) +1,2,3,4,5...
You can add any number of tools onto your buttonbar, or assign hotkeys for them, just pass filenames from panels to them using corresponding parameters.
I think that if you want to choose compare tool on every compare process, you need some proxy tool that will choose desired comparer, or if you want to compare using different algorithms, you need some compare plugin.
Also I think that 'suggestion' should contain exact description of some feature and not only abstract words.
If you use internal viewer, you can choose with 1..7+A+S+V between different options, how to see the file. The same procedure can be used for the comparing tool to compare different file types with different options or different compare tools behind the buttons.
As the developer of the LogDiff tool Romaschka mentioned, I could add support for loading input files from the command line if this would make it easier to start the diff from Total Commander.
patraulea, command line support is always great feature, especially if logic allows it. In your case it does - simply pass two filepaths in command line (maybe with some /options before). Since TC allows to pass names of selected files, it is quite useful.