This is quite an objective question and one that has been addressed quite a bit under various topics.
In my opinion, the most elaborate and realistic styles of the keyboards that I have heard are in the Ketrons. Technics are also quite good, though the Ketrons seem to sound more "live".
Yamahas are very useable, and more versatile as far as using one style for various songs. This is because they have always been LESS elaborate and more basic. Yamaha has shown signs of change in some of the recent offerings, including the PSR2000. Some of the styles in it, and in the CVPs, do approach those of the other companies.
Korg PA80 has some really great sounding styles, but are lacking in depth in many genres. I do a lot of Country/Western, in addition to other types, and the PA80 has a few excellent country styles. The PSR2000 has maybe 10 times as many useable C/W Styles. The opposite is true on Blues type styles. The 2000 (also 9000) has a few good ones, but not many.
I have yet to see any of the other brands that could touch Technics in the area of Big Band, Swing, Standards styles. They offer both variety and quality in these areas.
The only way to really tell which keyboard suits you best, is of course to sit down and spend several hours with each one. Not always possible, unfortunately, but that's what we SHOULD do.
DonM