I haven't tried the KN, but I tested the other 2.
I personally like the Korg better, better styles, much better sound.
I have and always have found Yamaha Arrangers (especially the lower and midrange models) sound quite synthetic.
Korg however, sounds to my ear more natural.
I can't help it, whenever I hear a PSR I think "Yuk!, this thing sounds like a toy synth", some sounds are pretty good, like the Live! Grand Piano, but the majority of the voices are
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.
But then again sounds are subjective, so you gotta choose for yourself.
Greetz
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,
Marcel