As others have said here, it's a matter of taste and in some ways like going into a bakery and choosing some great desserts. Being like a kid in a candy store, I went for Standard right off, got a bunch of pianos and then got more later on. It's not like you can't get others later if you want, besides, they are pretty inexpensive considering all the work that goes into the modeling of these fine instruments.
The NY Steinway D, Classical Recording, is that, well, classic Steinway sound that we know very well from all the great recordings and concerts. The tone, being American, is rounder and plain-sounding but in that typical Steinway way, whereas the European Hamburg Steinway is clearer and brighter, which is typical of the European pianos.
The other pianos have their own personalities and qualities with some being closer and more intimate, while others are brighter and bolder. Of all the pianos, The Grotrian Royal is my least favorite, and much like the Grotrian I played at a friend's house a number of years ago. Being very plain, however, it's a good starting point if you want to play around with other features found in Standard and Pro such as the layering where you can take two or more different pianos and combine them. I did that with the two Steinway models and the sound is unreal. It took a bit of tweaking, but I got a NY sound with the clarity of the European pianos.
Now I do recommend the free stuff such as the antique pianos as well as the other antique piano collections for purchase. These are quite different, yet very familiar at the same time. Having played real ones, I was quite impressed with the sound and I find myself playing the music for the period on the piano much like what is done at a piano museum I frequent. Chopin on the early Pleyel or Erard, Schumann on the 1850s Streicher, etc.
I hope this helps a bit.
