As said everything is subjective but I have a Privia 350 and love it. Played thru a good sound system, I hate onboard speakers. I didn't really give too much attention to the Yamahas because weight was a big factor for me. The lower end Yamahas were toys in my opinion and for the money the Casio won out.
The PX5S is more for use as a controller keyboard with four programmable zones and lots of other programming options. The 350 has speakers, some simple backing styles and is a good all around home or gig keyboard.
Buy what sounds and feels good to you, you've got to play it.
BTW when I was learning piano tuning an old pro told me that in NYC Steinway has a floor dedicated to their TOTL concert grands. Artists coming to the city to preform can go their and play as many as they like till they find one they like. Now thats really personel taste to the max.