Woodsman, when you say you have a chance to hunt either, do you mean you have a place to hunt in either location?
If you have someplace to hunt in Hettinger county, basically we are talking the Mott/Regent area, then go for it, more phez than you can shoot in a lifetime.
While even though Hettinger county has lost some CRP acreage over the last few years, there is still enough to hold lots of pheasants. Some public ground is available, but so to will be the extra pressure that goes with public ground in a Pheasant rich environment.
Have not hunted Mobridge but based on what the SDG&F is saying, the numbers there appear good as well.
If you won't be hunting Private land I would take a look at the amount of public land in each area and make your decision off that. The bulk of Private land hunting in those areas (especially Mott/Regent) will no doubt carry a trespass fee.