I really don't think it matters. But for resale value of your home, the concrete pad is better. Don't know where you live, but before pouring a concrete pad, make sure you are compliant with any zoning or HOA laws/rules.
We lived in town, and I wanted to pour a concrete pad. The spot was very muddy and slippery anyway. I thought it would be a great cure and provide a spot for the camper. I DID talk to the zoning office people and they said to pour a concrete pad would take all kinds of permits and design plans and all of that and a bunch of money to file everything. Then it would have to be inspected, meet all the city guidelines and by the time I got done just listening to what I had to do, I was exhausted and hadn't even left their office yet!
Then she said, but you can put down gravel anywhere on your property and don't have to have any permits or anything. The only rule was, the gravel could not spill on the neighbor's property.
I asked, what's the difference between the concrete and the gravel. She said, the gravel is temporary and can be removed! OH.... I learned something that day.
I went with gravel.
I put the gravel in, had a great spot to park the camper, and the mud was never a problem again. I always kept the tires on treated lumber. Never a problem.
When we moved to the country, our camper then parked on asphalt. As far as the camper goes, it made no difference.
If you can afford it, and you'll have no repercussions from zoning, concrete is the way to go. But your crushed garnet will work just as well (as far as a place to park your camper.) You won't have weeds growing in the concrete, and you can easily sweep of leaves and shovel snow (if you get any). Gravel, or stone is not so easy.