To me, they are just different. All the instruments are about equally good in the end, but the difference between them is very clear. Some will prefer Yamaha, some Korg, but it is absolutely just a matter of taste. Yes, Korg might be clearer in sounds, Yamaha might have more articulation, but in the end, both are fantastic. But different.

It is really about what makes you happy or inspires you. With neither you can go wrong.