Well out of all the major nations these 4 countries all have top fast bowling stocks, which argue well for the future of the game i think. Without reading to much i would be tempted to say Australia slightly but if i really think about it one can't be too certain. So i had a look:
All full of quality, as i said i'm tempted to give Australia a slight edge due to how consistent they have been over the years & the recent introduction of Troy Cooley. But England & South Africa are probably just as good on paper TBH.