Rbh
I think the NI definitive Piano Collection are the same sample sets of the Classic Piano's from way back. It has a Bosendorfer, Yamaha C7, Steinway, and an Upright of some flavor. Somewhat uninspiring to my ears after all this time - but they aren't bad. I picked them up years back for about 100.00 on a closeout before they ported them to Kontakt.

"NI definitive" as far as I understand were made by Galaxy instruments and sampled fairly recently?
 
http://www.native-instruments.com/en/products/komplete/keys/definitive-piano-collection/
http://www.galaxy-instruments.com/dpc.html
 
See especially Lemmi's comments here as well:
 
https://www.gearslutz.com/board/product-alerts-older-than-2-months/951994-galaxy-instruments-definitive-piano-collection.html
 
 

I have checked so many of them:
 
SampleTank3 - excellent stereo samples, some over 1Gb,
Sonar's TruePianos -  equally great ,
Addictive Keys, decent but a bit muddy
Miroslav Philharmonic - fantastic
 
but in my case the winner is EZkeys from Toontrack, crisp, articulate, beautiful resonance