Vocalizers:
Roland G70
Korg(only the TC Helicon)
Ketron ( Good but quirky )
Yamaha doesn't qualify for this category & needs to totaly replace the unit in their KB's period!

Styles:

Very Useable, Smooth fills/breaks/generic & repetitive:
Yamaha

Punchy/live Sound:
Ketron/Korg/Roland

Swing/Latin:
Yamaha/Korg (swing) Ketron/Korg Latin

Sounds:
They all have terrific engines now...
each with different strengths & nuances depending on how you play them.

OS:
Roland Touch screen/makeup tools
Yamaha
Newer Korgs
Ketron tie with Korg once you get the idea on how they work.