Soundwise the Casio's will win the competition. But the styles from Yamaha are imho far better to play melodies on then the once from Casio. I've had the WK3000 and the MZ2000 and sold then again because I could only play decent songs with a hand full of styles, the rest I couldn't get the right rithm. But others will disagree. The best thing is to play the machines yourself and then make a choise.