I've been a Roland man for years, but for pianos, I'd have to say that Yamaha does a better job. I really think they did a nice job on the S90 and Motif pianos. They aren't good enough to make a solo classical piano album out of, but it would be difficult to distinguish the difference in a multi-timbral multi-instrument composition.
SK880, sure, quality is relative, but the huge number of patches on these boards to impress people is over the top. Even the S90, whose pianos I praise, could probably have done better giving us 2 pianos instead of 8.