I had this same decision last December. Ultimately I chose the HR because it was significantly cheaper.

As said above, you can access the grand directly from terminal D, ticketing area (around D30, i believe). Can't be any easier than that.

If you go with the HR, take a ride over to the C terminal, and then you walk across the parking garage. I think C18 or so is the gate you want to exit at. Once outside, there are signs. It's maybe a 5 minute walk, and you go up/down about 3 sets of stairs. Also super easy, unless you have a ton of luggage, or aren't the most mobile.