Every year KOF improves its style, adds characters and creates a different story with a variety of fighting techniques.
KOF 2004 (and 2009) are my favorites, because they put every character into the fitting spot, so there are no true advantages against others adding a balance type of fighting.
If you are a fan of the saga and dislike the fact that some character have several skills which are mostly unbetable, this is your title!