My first trip to KS was last season, and I'm going back again this year. We hunted WIHAs near Wakeeney and Hill City, with good success. We waterfowl hunted in Cedar Bluff and it was excellent. However, I hear that Cheynne Bottoms is better. I would say if you are not afraid to drive Hays is fine, but you will loose hunting time driving. Great Bend would put you closer to ground zero in my limited experience. I never made it to GB, but Hays is the only area I would call a city near I-70 (if you need conveniences). I drove through Webster, but wasn't nearly as impressed with the waterfowl action as I was in Cedar Bluffs. Again this is based on my first and only trip to KS, with six days of hunting and 1,000 miles on the truck just in hunting mileage.
The bottom line is you won't go wrong in either area. Your waterfowl hunting will be over in two days b/c you will have maxed out your possession limit. Focus more on upland, with waterfowl opportunities within driving distance.