Agreed. I have to say, for the most part I keep running in to issues with Jython which I don't with JRuby. Note that Jython has focussed on language compatibility, and that doesn't include stdlib compatibility. That's where almost all my frustrations with it have come. Stuff just doesn't quite behave the same. Plus a number of major libraries, like Twisted, won't work on it for what on the surface seem to be bizarre reasons (https://twistedmatrix.com/trac/ticket/3413#comment:41 was the state of play 9 months ago and isn't changed now, you can see other conversation around problems with Twisted here http://bugs.jython.org/issue1521)
JRuby has Charles Nutter. No disrespect to Frank, but Nutter has really been a champion for dynamic langauges on the JVM, out in front, pushing all the time (JEP-191).