I think you will find a lot of posts comparing directly Akoustik and Ivory if you browse the forum.
I use a lot the Galaxy, so I can talk a little about it. The latest update is very good (in K2). I have made my own patch blending recorded PD resonance + symp. resonance script and it works very very well.
The miking is less close than Ivory and Akoustik (the closest), but still closer compared to Old Lady. You can ear both body and room res. in the releases.
The sound has the warmth of akoustik and the shining of Ivory, It can appear less "dense" in the medium because of the miking and the "hard panned" stereo patch. Personnaly I blend center + LFO channels in addition to stereo patch for stereo use.
The recording of this piano is unique : warm sound and good sense of "space" in a great studio, but still quite dry. A good alternative between full dry/close miked piano and "wet ones"
PD resonance perform a little better than Ivory (and can be greatly improved putting your hands in K2...)
I like Ivory the most. Galaxy only sounds good if you use the surround programs and even then it's kind of sterile. NI AK is ok but to close mic and clean. Ivory has good control and the bosendorfer is nice. However, Ivory is still too close micd for my taste. Sounds like they put the mics less than 3 feet away.