It depends on which 'feel' I'm after. But here are the ones I use the most, lately:
Kontakt (Alicia Keys library), and in the past Truepiano: for the more classic/acoustic piano feel.
Korg M1: For the 90's house piano. Totally rediscovered this one again.
Nexus: For the more progressive house / pop dance like piano's.
But it's all a matter of taste too of course.