If all your after is the most realistic piano sound, then you may want to consider a controller and a softsynth. There are a few out there that sound pretty close. In terms of the models you mentioned, I think the Yamaha CP300 has the best piano sound. I would also eliminate the Fantom G. Too many people complain about the issues with it and the for the $ and your needs it wouldn't be a good buy for you. Some other keyboard models to consider include the Kawaii MP 8 II, The Roland FP4 and the Kurzweil PC3. This is only based upon the information you gave in your post.
In all seriousness you will probably get many others giving you their impressions. The most important thing I can tell you is this: Get out and play all these models! No matter what anyone tells you, the bottom line is the best model is the one that will work best for you.
QL is generally amazing sounding- it's in a whole different league than Ivory (at least this version), and Ivory is quite good. Ivory has always sounded a little unnatural in the steady-state portion of the sound relative to the real versions of the pianos, and QL resolves this.
Downsides to QL? You need a whole hard drive just for the library, and it has the ability to bring even a very stout computer to its knees very easily. If you ever thought Ivory was taxing on computer throughput, it's a walk in the park compared to QL. The PLAY GUI is still not quite there in terms of stability, whereas Ivory is very stable.
The QL Yamaha C7 is very bright, and mostly worthless to my ears compared to the Ivory C7. But the QL Steinway is to die for. Love it.
To the OP,
You might add the Kurzweil PC3X to your "look-at" list. I am assuming by your question that you are interested in a hardware based solution (although it would make a great controller for Ivory also).
I've had my PC3X for a year now, use it mostly in my shop/studio and largely for acoustic piano. Both the keyboard touch and sound are outstanding, for electronics. Plus - I can play it without having to turn on the DAW and load samples. About 15 seconds after the power switch is turned on, it is ready to go. Note that the amplification is as important as the keyboard. So-called keyboard amps just don't get it. Most of the pros that I converse with are using either studio monitors (in small areas with no moving around) or powered PA speakers, I'm using a pair of EON 15G2's.
The only fault I've found is that it is heavy to carry around for gigs. I was using a 2661 for gigging, but have just added a 76key PC3 for carrying around. Same great sound, a bit lighter weight on both the unit and the keys, still can play piano on it, or clonewheel, bass, orchestral, etc.