Hi,
tend to think it's a matter of taste and what you get used to.
Had to swap my yammi baby grand for a digital piano years ago. At the time the clavinova's sounded the best to my ears.

Over the years I've gotten used to the Yamaha piano sound.
Piano wise, I prefer my current YamahaCLP170 to my ex Technics piano. There again I preffered the piano sound on kn7000 to the 9000pro & Va7 . Never overly fond of Korg piano sounds, but there again the last korg arranger I had (i2) dated back to the mid 90's.
Must admit I haven't heard casio keyboards,
so I can't comment, but moneywise they seem a real bargain.

best wishes
Rikki