Just my two cents.
I owe a Roland with the Supernatural and, while I'm not overly fond of Pianoteq, I do think some of their instruments, such as the Petrof, the Steingraber, and the Bluethner, do sound better than my F107 onboard piano.
Following Stu Harrison's counter-intuitive advice (decrease touch sensitivity and increase brightness), tinkering with the tuning and so on, I was able to finally get a decent sound out of it. The mid range is still
a tad harsh but the highs are okay.
Then again, no onbord sound compares to VSTs.
I haven't tried Roland high-end modelled pianos and, as pointed out here and in other threads, I question Roland's taste in terms of what kind of sound they deem as ideal.
But, when I practice and have Pianoteq coming out of my monitor speakers, the improvement in the pleasantness of the sound is quite noticeable.
