Hitman101Hitman, without testing these, it's really hard to answer a question such as this. I can tell you from experience (I own Grado RS2e's) that the Grado sound signature tends to be on the bright side instead of neutral. You will probably find a lot of user feedback on the head-fi.org forums that can help you make a decision. Also, both headphones are very different in style, as Grado has a retro, minimalist over the ear design versus Hifiman's more modern style and around the ear design.
xZEROZxboth headphones have a bright sound
the only difference is the hifiman's are over the ear and the grado's are on your ears and tend to be uncomfortable over prolonged listening sessions. Get the hifiman's if you like over the ear/get the grado's if you like cans on your ears.