What's with this "The Best" stuff? ;-)
No such thing. SOme like software instruments like NI B4, Some like organs of the Phantom, Motif and Triton workstations, some hate emulations altogether and stick to using the real thing.

I think any decent KB workstation of today can take care of organ sounds. Surely there are dedicated organs as well. Most of us KB players tend to find the middle ground and go for workstations because they do a bit of everything and often do it well. To my taste Yamaha Motif Es has some nice organs and rhodes sounds but for real
authenticity I prefer NI B4 and Lounge lizard software instruments. However since I don't take a laptop to gigs I only tend to use software synths in a studio
environment.

Also, I don't use KB amps and instead prefer powered studio monitors (again, never had to take them to gigs) so you'll have to wait 'til others post. Also, since playing live is what you're getting ready for I suggest you post over at The Bar and General Arranger KB forums here. Don't let the word "Arranger" fool you. Everybody around here knows a thing or two about organ and EP sounds as well as live work.