If you cancel the Hammerfall to a Hammerfall Break you can PB, lots of people block if they see HF coming so they just stand there. It's a bit tricky to get the timing down but once you do it's awesome to get them off.
My favorite personally is backdash buster but it's not exactly aggressive.
If you are 5P, bustering you actually have to wait a little because if you do the buster too soon it will whiff. Not too long, but you can't do it instantly basically. 5P doesn't actually cancel into buster, it just has such a short active time it looks like it does. Basically, any quick moves can be used in place of 5P as well, lots of players expect to be thrown after a 5P though.