Sound: more realistic on the Roland. The Yamaha samples sound very "electric"; furthermore, there are very few samples per note, so you lose a lot of timbre.
Keyboard: the Rolands feel immediately more robust to the touch, less toy-like. It's a feeling that is difficult to describe; you should try it. What is left [to say]? For a pianist who has to play, having analyzed the keyboard and sound, it seems to me there is nothing else to add... In any case, these are personal tastes, I work neither for Roland nor for Yamaha...
I have a Roland RD 150 and it works perfectly: actually, now that I think about it, I need to open it to clean out the dust because there is one key that sounds and doesn't sound.
In general, in my opinion, Yamahas compared to Rolands have a heavy and less agile action. I can't understand why Yamaha makes them like this... I own a Yamaha U3 upright and the action is agile and light, whereas in the digitals it is quite the opposite. I can understand that a more pronounced weighting helps control dynamics, but this feels too much to me (I also tried a Yamaha CP300).