"Between Yamaha and Roland, you are looking at probably the two best lines. They both have a graded hammer type of action, as well explained by PIANOS007. They both have excellent sound sourcing, Roland uses different marketing terms than what Yamaha does, but they are both very good. They each have a different sound to them, it's really a matter of which you prefer. The primary distinction between them, in my mind, is the touch. Both are good, but because of the placement of the leafspring in Yamaha's action, it makes it feel a little heavier at the top, but once you get past the tensile point of the spring, it feels a lot lighter very quickly. I prefer Rolands mor e realistic gravity based approach, without the use of springs. That is for you to decide yourself on which you prefer. The polyphony leves are actually equivalent as Roland's 64 voice polyphony is equivalent to Yamaha's 128 note polyphony. (The distinction is that when using Yamaha's sampling method, two notes of polyphony are used for every one note of piano played; Rolands sampling method uses 1 note of polyphony for every one note played.) In the end, both will play the same number of notes."
From another forum, but I conquer completely.
Ron