I have always run a Harris but for longer hikes & backcountry hunts I have just shot off my backpack. That works OK but is not as stable. I have it narrowed down to the Spartan Javelin Lite or the Eberlestock Pack Mounted Shooting Rest.
Harris S-BRM - to which (over time) I've added an RRS Pro Clamp Adapter, KMW Pod-Loc lever, and Hawk Hill Customs feet... its great, but if I had it to do over, I'd probably go with the Javelin.