I vote SeaHorse Haven in the Sam Houston Nat'l Forest.
You can't camp overnight at McKinney Roughs - so you will have to stay at the Horse Hotel or something else and haul in and out each morning and night. Yes you have to have shoes on your horse if you don't have boots- your horse will be done for the weekend after about an hour of riding otherwise (been there done that). You also have to haul in your own water for the day and you only have about 15 miles of trail to choose from (the rest is off limits to horses).
Sam Houston Nat'l forest gives us access to 50 miles of trail, an enclosed private place to stay with cottage to hang out/eat/chat with and RV hookups with water (or water and electricity for a fan or heater if you want to camp in a tent) and the trail is mostly in the shade and you won't need shoes or boots on your horses. They also have pens to rent if your horse is inexperienced camping and doesn't camp tied. You can ride your horse right out of Seahorse Haven into the woods so you don't have to haul back and forth.
McKinney would make a good day trip, but if we wanted to camp for a night or even two, I'd rather have the amenities of SeaHorse Haven and their little picnic area with the fans and potty.
Neither place rents horses - no dogs at SeaHorse haven, tho.
Clippityclop is finally getting to spend some time in the saddle!