the poster was talking about ur favourite video format not quality, for quality OFCORSE uncompressed avi have the best qaulity but it is very huge in size, u couldn't store many videos in ur HDD if u use that, , and second best audio codec for quality is mpeg2 as i know (not 100% sure).
but my favourite video codec is wmv for two reason:
1- it gives quite good quality at very small size
2-it can be read by all kinds of media players in microsoft windows ( like realplayer, wmp, winamp etc)