Both places have its pros and cons. I have not been to kermit in about 3 years. The last day i was there was when the county came out and tore down the pavillions. I have not been to the campground the new owners built.
The sand at Kermit is finer than LS. The dunes are larger at LS. The bowels are larger at Kermit. You can go to the back section and ride all day without seeing anyone else. If you do go take a compass, I think the place is 25sq miles + and if you dont know the land marks you will get lost.
I hope this answers a few of your questions. Both places are great to ride, but they are both 5 1/2 hours from me. If you break down at Kermit and dont have extra parts you will be coming home sooner than you think.