Just recently replacing my old S910 with the SX900, voice wise I would say the preset voice is a jump (and iirc Korg's older keyboard doesn't sound that good compared to my S910).
Korg kinda win on customization, seems a bit more flexible than Yamaha but nothing really missing here with all Style available.
Personally I would prefer Genos, but the used price here is quite stagering (about 3000usd) and due to some pressing need with the church I decide to buy SX900. The Revo drum sound really cool on Genos (tho SX900 is no slouch, in fact compared to S770 that our church own I would say there is a bit of jump in quality). The DSP on SX900 is also a bit better, same preset voice sound smoother on SX than the older generation, tho I'm not sure is it due to better sample or better dsp. Price wise in my location the price is about the same as S975 when first released. I think in my country PSR Series are quite popular and it is also manufactured here (not the Genos tho, it is made in China) so overall it is cheaper here (about 1300 usd, additional 50usd for hardcase+stand).
The touchscreen need sometime to get used too (I prefer tactical button) but assignable button is a blessing, especially for toggling half bar fill. Controlling volume doesn't seems as intuitive as button based PSR-S series especially when the touchscreen doesn't support multitouch which prevent dropping multiple part volume (CMIIW, I only experimented with it for about 2 weeks)
Just my 2cent