That hasn't been true for a few years, but it was true for quite a while. At this point Pugs is fairly out of date and (I believe) abandoned, as it's main developer discontinued development. For a long while it was the most advanced Perl 6 compiler though, and from what I understand a lot of it's rapid advancement was attributed to it being written in Haskell (Perl 6 and Haskell share a good portion of advanced features, so that may have helped).
The current state of support of the various Perl 6 compilers can be seen here[1].
