I tested both UltraCompare and WinMerge, but removed them again because I didn't like their interfaces. I am not a coder and have absolutely very little to use this kind of programs for, so it is important to my IT illiterate brains that any "diff"-program above all is easy to use, and (only then) not too expensive. WinMerge is of course cheap (free) but the window is a little "weird", making it a slow process to read each line.
Remember that we are talking about two different type of files, M3U and WPL. The first song in the playlist will do fine as an example of the problem. In M3U it looks like this:
D:\Musik reserve\Plain White T's\-no album-\00 Rhythm Of Love - Plain White T's - .mp3
but in the WPL the same song is like this:
<media src="D:\Musik reserve\Plain White T's\-no album-\00 Rhythm Of Love - Plain White T's - .mp3" tid="{7FC85ED8-E4C7-43E5-9C6D-D03A51C7A432}"/>
-so you see, any diff program will *almost* show more differences than similarities!
I expect to maybe get a key for Compare It! if/when it gets on discounted offer
- but I have of course not yet made any final decisions. It is not urgent ;-)