I have never tried Parthia, mainly because of their infantry. Or lack thereof. Slingers probably would do just as well as EI. And it's not like Hillmen are putting any fear into people. I get that Parthia has good cav, I should probably try them out sometime just to see how it goes. I do prefer cavalry heavy army, but I like to have some infantry. At least to build a ram to knock a hole in the gate so my cav can wreak havoc.

And I love slingers against chariots, although I mainly use Rhodians or Baleric.