Slab on grade is a foundation that is back filled and concrete floor added, by far the cheaper way to go. A plumbing problem down the road could require digging up the floor but then you have to weigh all the pros and cons.
A crawl space may give you some dry storage and access to plumbing.
Where I am they both require a perimeter drain and second pipe for down spouts but the crawl space need waterproofing on the foundation with poly on the ground with a skim coat of concrete and min. height of 5ft, then you have to decide to insulate the floor and plumbing or seal the space, which has a bunch of other questions. Either way the crawl space will need to be checked from time to time adding to the yearly maintenence list.
The slab on grade has different insulation rules in different places, sometimes rigded foam under the floor for some distance around the perimeter and others have the same foam inside the foundation right up to the floor level.
With slab on grade a hot water heated floor is a really good option, the normal is to insulate under the whole floor when the floor is heated. The last time we had an extended power outage, I was in a house that had that kind of heat, I questioned why the floor was still warm. He said he didn't insulate the floor and it warmed the sand below and when the boiler isn't running it take two or three days for the heat to stop coming up, I question the extra cost of heating the sand. He said not really much as you only heat once when you start up.