UltraEdit is definitely the best text editor for Windows, but its built-in comparison utility is a bit simple, WinMerge and KDiff3 are two best free and open source file comparison software, you can integrate UltraEdit with them easily, there are just two steps:
1, Open the file named UEdit32.ini with UltraEdit or Notepad
In Windows XP the file is located in this folder: “C:\Documents and Settings\ Your username\ Application Data\ IDMComp\ UltraEdit”.
In Windows 7 the file is located in this directory: “C:\Users\ Your username\ AppData\ Roaming\ IDMComp\ UltraEdit”.
2, Add just one line to UEdit32.ini
Find the string “[Settings]” and add the following line to the [Settings] section:
Compare EXE=”C:\Program Files\WinMerge\WinMergeU.exe”
Compare EXE=”C:\Program Files\KDiff3\kdiff3.exe”
Then save the file and restart UltraEdit, now when you compare two files opened with UltraEdit, UltraEdit will call WinMerge or KDiff3 to fulfil the comparison task.