I myself have a yamaha keyboard and like yamaha very much. But at your price range, I think you should open yourself to some other brands as well cause I'm almost certain you won't get the same bang for the buck with yamaha.
I recommend trying out the casio px130 or something within the privia line at a local store. I prefer it over the keyboards you've listed cause it has a more real weighted action keyboard feel than the ones you listed. You don't need better weighted action if you want to do mainly synth sounds and stuff but if you want to play the keyboard like a piano (with some notes played much softer and some much harder than others), you really can't do that well without a good weighted keyboard feel.
It sells for $500 at guitar center but if you try to get on their mailing list, they very frequently mail you 10% off coupons - it was 15% near Thanksgiving. Guitar center has tons of keyboards so I definitely recommend you test some out there even if you end up buying yours somewhere else.
Buying off craigslist.com can also save you a lot of money as well.
That said, both the NP30 and YPG 535s are good keyboards as well.
