Welcome to the forum.
I am a guitarist/bassist not a pianist but JonD is my keyboard player. I have a number of piano VSTis but we using them in songs. This is totally different than a solo piano where the piano must sound as realistic as possible.
Maybe this 3-page thread will help:2
http://homerecording.com/bbs/equipment-forums/midi-mania/best-piano-vst-instrument-189406/Google/bing piano vsti and you will find them from free to expensive. But
IMHO to get a somewhat realistic piano VSTi you will have to spend some money. I say that because MIDI can fool an audience but it but it has to be a very good VSTi and played by someone who is knowledgeable about that instrument to fool a musician that plays that instrument. That is what you are finding out.
I also play a wind controller and I have some great sax sounds from samplemodeling and some excellent flute sounds from various companies. I have fooled a number of people using these sounds but I have never fooled a sax or flute player.
Good luck.
{edit} John and I were typing at the same time. He brings up a very valuable point. You must have good speaker monitors. Near field monitors with as flat a response as possible are the best.