My go-to method, given an excellent hall and excellent piano, would be AB stereo for solo piano. Nothing more, nothing less.
More microphones introduces phase issues or worse, double attacks or double resonances.
It was Yannick who warned me for that, and he was absolutely right. Where he swears with MS, I am too much in love with spaced omnis, because I do not want an accurate image of each piano string. (Even with some ensembles positioning is not a priority for me)
Perspective is, and balance and width. I think I adjusted my initial setup for almost one hour while the performer was warming up, to find what to my ears was the best position/spacing/direction of this AB pair of DPA 4006TL modified by Rens Heijnis.
Enjoy:
https://www.youtube.com/watch?v=ewhDir6Vk4g and
https://www.youtube.com/watch?v=4dcpgQtGdLw or
https://www.youtube.com/watch?v=GD6VWB7HVoE
In the first link, you can see the setup in the shot from behind the piano.
Another example, this time on a Fazioli 308 beast:
https://www.youtube.com/watch?v=boys5vjvYwI
In less stellar halls for a solo recording, I will often blend this with a closer pair of cardioids (Schoeps MK4 or Neuman TLM67 or Brauner Classic), each microphone delayed exactly to the corresponding microphone of the main AB pair.
For chamber music, the main pair will mostly be dictated by the sound of the ensemble in general. Here I am fan of a Decca tail pair (mostly KM183) for piano support, as it is less bright and mostly blends very well.
https://www.youtube.com/watch?v=bijX7TK4nl0
Only in rare situations, such as here with a straight strung concert grand, this Decca tail pair does not 'work', and I have to search for another approach. Here, a classic LR spot pair was ideal. Notice also the ribbon pair (Rode NTR) for the cello, with an extra omni spot close to the podium for extra bass reflections -- the hall was not very bass-friendly.
https://www.youtube.com/watch?v=3b0KjWthKCY