For now I have to live with Visual SourceSafe… grrrr.
I have problems with files that it cannot compare, so I searched for a solution and found one that shows how to change the Compare tool.
I am using Kdiff3 as I already had it installed.
Visual Studio 2013.
Goto: Tools | Options | Source Control | Plug-in Settings
There select tab Custum editors and then click Advanced:
Add the path to your compare tool followed by %1 %2 for the 2 files to be compared:
D:\program files\KDiff3\kdiff3.exe %1 %2
For Operation select: File Difference.