In the sailing world one has the option of blocks (pulley assemblies) with plain bushes or roller bearings. Anything where the line through the block is normally static uses a plain bearing, those requiring continuous adjustment benefit from roller bearings. The plain bearing provides greater support area but slightly more friction. Although you can use a roller bearing on static applications, they tend to deteriorate quickly as any vibration frets away at the fixed position of the ball or roller making them rather rough in operation.
Taking those design parameters to the keyboard, a mechanical bearing would be expected to be superior at first, but prone to failure. I suppose the ultimate would be an Oilite bearing, sintered metal which holds lubricant in its sponge-like structure.
Rob.