If you're looking to have more options (especially in the number of NON piano related sounds that could open up more possibilites musically) on a digital, I'd say go for a more recent Privia model. Action is going to be a subjective issue as well. I'd say the most obvious thing that stands out to me with the piano samples on the Privia models compared to the Yamaha models is the Privia's pianos are "warmer" and the Yamaha's have a "brighter" sound.
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GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.