I don't think I've had a chance to ever demo the RS1. I've heard that it retains the detail of the 325 but with less sibilance and a generally more balanced sound. I suspect the difference in sound might be more due to the mahogany than the driver, but who knows. Also heard good things about the HS2. I kind of wish I jumped on those while they were in production but I was a little strapped for cash at the time.
Besides the grado lineup though, I've never heard a can that approaches the detail of some of the Grados. Maybe stax?