Best thing to do is to get demos for the VSL pianos you are interested in and try them out to see what you like most before buying.
They're currently (at least as of today) offering free 30-day demos for all of their Synchron pianos on the VSL website - I would grab demo licenses ASAP because the open demo period will likely end in the near future. I believe that once you get the demo licenses you can activate them and try them out at your own leisure.
Having said that, I've tried all the VSL Synchron pianos pretty extensively and currently own all of the Grands which the exception of the Fazioli and these are my general impressions:
Yamaha CFX: Probably the most balanced and versatile all-around, and the most likely to appeal to a broad range of playing styles and repertoire. Apart from a few very slightly out of tune notes in the upper register, it has no real glaring flaws I can think of, and many strengths.
Bosendorfer Imperial: This competes with the CFX as my overall favorite, though it really requires the full mic set (particularly the ribbon mics) to get the most out of it. Very rich and clear tone with a big sound that scales up powerfully but also responds to a more delicate touch. Great playability as well.
Steinway D-274: Very faithful capture of the signature Steinway sound, but also a bit more fussy to control and dial in just right. It has the most tonal variation with a very rich sound that excels in the softer velocities and blends better than the others, but can be a touch harsh at louder velocities. It's still a very strong instrument that does certain things better than any of the others.
Bosendorfer 280VC: This has an extremely clear and crisp sound profile, although it can be a touch glassy and hard at the top end. It's the only modern grand recorded in the smaller B stage which really makes a difference in the sense of closeness and intimacy. I initially had very mixed feelings about it, but have really come to appreciate the clarity and immediacy that it brings - for me, this one feels the most like having an actual piano in the room with you.
1895 Bluthner: This is more of a character piano with a very unique sound unlike that of a modern grand. I happen to love it, but it has very specific use cases and will not appeal to everyone. Fantastic playability and realism though, and worth trying out just to see how you like it.
Fazioli F308: This was my least favorite among the grands by a pretty wide margin. On the plus side, it has an extreme amount of clarity and evenness. On the negative side, I find the basic tone be blunt, colorless and dull, the bass region to be weak and underpowered, and the soundstage to be curiously pinched and narrow in comparison to all of the other grands. But this is just my opinion, and if the sound demos appeal to you, it's worth demoing.
Both of the uprights are also really nice, with the Bosendorfer being my personal preference.