Let's see...
1.
Piano Collections Final Fantasy X
2.
Sailing to the World Piano Score
3.
Okami Piano Arrange
4.
Piano Collections NieR Gestalt & Replicant
5.
Piano Collections Final Fantasy VII
For me
FFX defines the perfect piano arrangement. The main reason is the consistent flow. It's not just a bunch of arrangements thrown together -- the whole album is a single unit. Also the ending theme gets me every single time
Same reasoning (flow) applies to
Sailing to the World and
Okami. I could probably listen to these on repeat and never get tired
The
NieR and
FFVII album are beautiful in itself, even without featuring this kind of "homogeneity".
There are also some nice piano albums of compilation type, like the
feeling wind one for
Wild Arms, or the
Suikoden ones -- which however, due to focusing on many titles, are much more "heterogeneous".