In my experience, OpenJDK has fewer bugs - at least the ones I care about. Like Swing making bad assumptions about the WM, including that only a small fixed number of window managers are tiling (OpenJDK works on XMonad, Java 6u21 does not).

FUD. They're pretty much the same code base. Also "Moving to OpenJDK as the official Java SE 7 Reference Implementation": http://blogs.oracle.com/henrik/entry/moving_to_openjdk_as_th...