Most of them have several styles per type of music. Yamaha styles are more basic, and as such are quite useful if you play pretty well, and can do your own riffs and fills. Ketron and Korg styles are generally fuller and more, well, stylized. If you use the same Ketron or Korg style several times it does become recognizable as a style.
Yamaha has the largest variety and number of fill-ins, intros, endings and breaks. They allow the user to customize on-the-fly as you play a song. Korg has only 2 fill-ins per style and they are not very well-done as a rule. The Korg Break is next to useless.
However, the Korg styles are generally longer, running 4-16 measures and have more variety built in than Yamaha.
Ketron is sort of a really good mix, with considerable fill-in and intro-ending options, but also with full, intricate styles.
The Korg vocal harmonizer works only in Vocoder mode, and does not work in Chordal Mode, the one that many of use.
Technics, at least up through the KN6500, has a microphone input, but it is really bad.
Yamaha has the best mic processing, DSPs and vocal harmony, IMO.
I feel Yamaha's operating system is easiest to learn and use, and Technics ranks right there with it. There will be a rather steep learning curve with Ketron or Korg.
These opinions are worth what you are paying for them, but they are the result of pretty extensive use of all the models mentioned.
DonM