I prefer Pianostreet because I do not wish to restrict myself to the subset of piano music known as "classical". Even the division into "classical" and "non-classical" on Pianoworld seems to me unnecessary and more of a hindrance than a help. This is because clear-cut divisions into categories do not exist in my own mind and I often find it hard to know where to post an idea.
On the other hand, if somebody is interested in just one aspect of piano music - classical, jazz, how fast you can play or some other subset - then one of the other forums might be better than this one. I am eclectic, but that in itself is just a personal choice.