Community question: Which city has the best street art scene?

I just wonder, where can we find amazing art on the walls outside the UK, here I can find almost everywhere. I know about New York, Berlin, Budapest, but would like to know more, so drop it here in the comments.

By the way, come to Bristol, for the biggest street art fest in Europe, (but UK is not in Europe anymore), Upfest, and meet me there!