First off, you need a good base and drainage. It is impossible to determine what needs to be done in your case without knowing what kind of base you currently have. If you have a clay base and suffer from water issues, you need to build a good base and drainage before you even think about concrete strength.
lets as an example say you have a sandy loam condition that is currently a grassy area and you want to make a concrete pad to park your motorhome on. First you need to excavate all the sod and decomposing matter so you can get down to a solid undisturbed base. Then you are going to want to bring in 6" worth of 1" crushed stone or crushed concrete and have it vibrator compacted. Now you are ready for rebar, mesh, etc, make sure it is installed on stands, just having the concrete guy pulling it up into the concrete as he pours it won't do because it will get pushed back down as they walk around in the concrete. Once the rebar is in, you are finally ready for concrete, be forewarned though, that the amount of water and the length of time the concrete has had a chance to cure while in the cement truck will make a difference in the final yield strength.
Here is an article that will give you some idea on what is involved in determining concrete yield strength.
What I would suggest is find out how much weight you plan on putting on the driveway. i.e. the weight of your fully loaded class A motor home,
Get apples to apples detailed bids from several REPUTABLE concrete conractors on what strength concrete they will be using, what size rebar and on what centers, how many layers of rebar, etc.