Until recently, the two front runners in the virtual piano race were TruePianos and Modartt PianoTeq. TruePianos was slightly more affordable and was generally thought to be more playable and realistic, while Pianoteq, although an impressively flexible and powerful piano model, suffered from artificial overtones. Since Version 3 of Pianoteq, this is no longer true, in my opinion. Pianoteq has seen some impressive upgrades and options and is definitely worth the additional expense, and these days I use Pianoteq in my projects most of the time I need a piano track.
However, I've kept TruePianos installed. It's still a very inspirational virtual instrument.