You didn't say who your traveling companions are and their tolerance/comfort of road-time?
If we're road traveling (without camper) we try to leave early. Adults grab a cup of coffee, maybe a piece of toast to soothe the stomach gremlins, and the kids drag to the vehicle with pillows and/or blankets.
Most of the time we drive about an hour, then check the state of consciousness in the back. If they're awake, stop for fast food and restrooms. If not, another 30-45mins and stop before we hit the Turnpike.
It allows us to get a little distance under our belt while the kids get to rest and avoid the sleep penalty.
Then I can drive until lunch, which sometimes is early, sometimes later, depending on how everyone feels. As we look for lunch, I try to hit a gas station at the same time, then I can wash up and we go in for a sitdown restaurant lunch- or fast food if we have lots of distance to go. THIS is where hauling the camper is different. We will have the option of pulling off somewhere and going into the camper for sandwiches, walking around, etc.
I try to make sure we stop and get everyone out walking every 3 hours at least. Not just for restrooms, but circulation and cramps are greatly reduced, just by walking into and around a convenience mart.
For this year's big trip, we are planning on traveling into the night while the kids sleep and pull over and move everyone to the camper at a rest area or whatever. The goal is to allow us to have a leisurely start in the am to arrive around lunchtime or so at our campground destination, look around a bit, grab lunch, get travel/tour maps, etc and then be ready at checkin time to park our camper and setup.
Hopefully, it will allow everyone to get to the CG and settled just before the crankiness sets in. So that's somewhere around 6-7hrs the first day, and under an hour the second day. About 600 miles to our first stop for 2-3 days, then about the same to our next stop.
We also avoid rush hour. If traffic gets bad, we stop for lunch or whatever. I'd much rather drive longer into the night than sit in stop and go traffic ;)
When we have longer distances, I'll drive 10 hrs in a day, but by the time we arrive, everyone is wiped out and we just eat and crash and start our day in the am. 6hrs is fine, 8 is doable, 10 is pretty much the limit unless there is some major push, then it is a Dad's job to give up his rest and drive while everyone else sleeps through the night :C
I've driven 24hrs straight, but not with my family. They are too important to push that long.
So far this works for us and is the plan for the upcoming trip(s).
Hopefully it will give you a picture of our situation and help you pick what is right for you ;)