Like any two implementations of a spec, they probably have different performance and stability characteristics. As for what those differences actually are, or

Like any two implementations of a spec, they probably have different performance and stability characteristics. As for what those differences actually are, or if there are others as well, I'm really not familiar enough with Harmony to say. My completely unsubstantiated guess is that end users will be more interested in OpenJDK, as it's derived from the mature, battle tested jvm Sun's been shipping for years.