DickieFunk,
Its impossible to deduce what you have in mind and what kind of tone, you would be satisfied with, cos these things are based on culture, and your own personal experience, and personal preferences.
There are however a couple of objective things that are somewhat easier to, dare I use the word, measure, evaluate, be confident about, in comparing piano sample based libraries.
1. Obviously Cost - and from the tone of your initial request, you are definitely thrifty and value for money is key.
2. Opportunity to hear these sample libraries played by others, and preferably by a good number of demonstrators, so you can reduce your risk of buyer regret and the potential for feeling bad about your purchase. This is especially important in today's world, cos with software and data based products, predominantly, the sale is final, and unlike a hardware keyboard, you cannot return the product. (well there are a few exceptions - see below).
3. Reputation - Its a bit difficult for a large number of people (and I do not here include "paid" endorsers and celebrities, but ordinary folk who have not been paid to promote a product, and their genuine feedback is relatively unbiased - partly why you ask this question on GS.
4. Product Reliability - how stable is the product or the sample engine such as Kontakt used by the product, and what is the likelihood that any bugs will be fixed.
5. Playability - In your case as an accomplished musician, I assume you will be playing these samples and recording them into your projects or live on stage, rather than looking at a score to create the MIDI, so it would be really important to have the velocity mapping between your keyboard and the sample layers in the library, well adjusted to each other. Generally the sample libraries with more layers, do much better to enable a seamless timbre transition between low velocity and high velocity, and where you are able to also make adjustments to this velocity mapping, to better suit your controller keyboard, the genre of music, you wish to create, as well as your own personal touch preferences - which sometimes changes over time as you become familiar with the sample library, this ease of velocity mapping adjustment is an important usability feature, that can be compared.
6. The sound - how well were the samples captured, free of undesired noise, and what effort has been made to provide decent sounding pre-made microphone mixes, so that you can be up and running from day one, or are also able to have a good number of microphone positions captured, that allow you to mix your own custom sound, that best fits each of your projects, purposes. I mention this cos you speak of the need to have a single piano or set of pianos which can adapt. A lot of this ability to adapt the sound of a piano, revolves around the availability of multiple microphone positions, which the end user can tweak, to taste. This bonus is both a potential advantage, as well as a potential nightmare in the hands of those who really have limited skills in mixing, cos with great power comes the need for great responsibility. Some tools are the opposite of Noire, which you have since acquired, which has no additional microphone positions, and only a choice of a normal and a felt set of samples, which may just be what you need, if you like the sound and can use some of its other controls to achieve what you have in mind. The microphones and recording chain used, have an important contribution to the sound, and any ambience controls provided, such as algorithmic or convolution based reverb, will also add their own flavour to the dish.
When it comes to the sound of a sampled library, one has to think of context, and by this, I mean the age of the piano, cos piano sound has significantly changed as more modern methods have been developed over time. For example if one wants a Steinway D sound, there is not one, but a variety of tones, depending on the time of manufacture. A 1905 Steinway will not sound the same as the similar model manufactured in 1990. A Yamaha will not sound the same as a Steinway or a Bosendorfer.
Are you seeking a grand sound or an intimate sound like an upright?, do you want lots of ambience or very little? Tuning and consistency of tone - do you want a perfectly tuned piano, or one with a few quirks left in, to avoid it sounding like a machine? The beauty of any man made instrument is that it is not perfect, and these imperfections make it sound even more natural and authentic to the ear.
I give an example, in pop music you probably want a perfectly tuned even temperament, low dynamic range kind of tone that will punch through and compete well with all other sounds. In jazz, you may prefer a more rounded tone with less attack, and more sustain or less sustain, according to the kind of tone you have in mind for the piece.
As an example there is a stunning really unique piano tone on this recording, which is absolutely perfect for the piece, a genuine Steinway
D, but this would not be suitable for some kinds of music, with its amazing rounded minimally percussive tone. By the way this is one recording/video that stuns be every time I hear it, music from another world, outside of what is considered popular but its amazingly good music and musicianship/recording and mixing.
Classical music would need something a bit more dynamic and percussive
Next would be trad jazz,
On the other side of the piano tone spectrum would be highly percussive tones, used by people like Joe Sample, Chick Corea, Hiromi.
And on the really percussive other side would be the kind of pianos used by Elton John, or Coldplay, where its all attack and less sustain.
This is already a long post, and I still have many thoughts unspoken, so I'll follow up in the next post