I have to go with Ivory II Steinway all the way. It is so realistic that I can smell the wood when I play a note. I use the Ivory II Yamaha on some country stuff that needs a brighter sound. The Bosendorfer is great, but I don't use it. I know jazz people who love it.
If all I had were True Piano, I would put it in a track with pride, but there is no way it can match the huge sample libraries behind Ivory II.
I often use Ivory II's built-in hi shelf EQ on the Steinway for pop music. In the old studios on a real Steinway, I would get cramps in my hands and wrists from hitting the keyboard as hard as I could to get a bright sound even when the piano was going to be mixed gently in the track. Recording Ivory II at higher velocity replicates this and the hi shelf EQ gives it a little more sparkle.