itunes all the way. one click and everything is organised. wmp just confuses the hell outta me. though i use it for movies, which doesn't need organising at all.
i use itunes for various reasons, although, mostly just cuz it organizes my files far better than WMP or anything else i've tried.
i use a bit of all lol. but usually if i'm playing music prob just wmp as thats what opens when i double click an mp3 file.
For me... Videos : Media Player Classic Music: iTunes [Also WMP 11 when i don't want to add songs to my iTunes library ]
I use WMP 11 for music and RealPlayer for videos. but i use iTunes sometimes to put songs on apple devices.
for music listening I use windows media player, but recently i discovered I prefer MediaMonkey more. but for videos i would be using KM Player, it's a korean player
i only use itunes simply to transfer my MP3 songs to my iPhone but most of the time i use VLC for Video and Media Player for Music