As far as I know, the best acoustic pianos among all the workstations are on the Yamaha Motif ES and the Fantom X, while Korg is more geared towards synth stuff (I am leaving aside Kurzweil because it's more expensive).
Maybe you should check out the Music Player Forum; there are a lot of threads dealing with questions like the one you asked here.
Good luck!
http://www.musicplayer.com/cgi-bin/ultimatebb.cgi?ubb=forum;f=18
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Korg Kronos 61 and PA3X-Pro76, Roland G-70, BK7-m and Integra 7, Casio PX-5S, Fender Stratocaster with Fralin pickups, Fender Stratocaster with Kinman pickups, vintage Gibson SG standard.