Although it has a fair number of options for tailoring the sound, I find myself sticking with a single rich grand piano sound. Ivory II - I think this has the best pure grand piano sound, and is what I use 80% of the time when that is the sound I am after.

I think they all have their strengths and weaknesses, but these are strictly my opinions, not necessarily backed up with extensive resesarch. I use both of those, along with Keyscape, and almost all of my use is in live performance.