For the reasons both TG and Phantom mentioned, I like the H41 more for grinding; the J39 I have because of my KM collectors fever :) It is not a bad ship (the J39), but H41 has almost the same range with more speed, which is indeed the key to survive in a KM ship (hit&run techniques, ninja techniques, etc.)
I still havent seen J39s in any HA...
Hope this answer your question!
Ade