Technically, toluene should be used for hypalon/csm/neoprene surfaces. It is typically a similar solvent to what is found in the glue, and it is not very aggressive. It can be used for deactivation and reactivation of the chloroprene glue used for bonding those types of materials.
Same for MEK, it is specified for use with PVC/PU. It is also similar to what is found in the glue, so it can be used for deactivation and reactiviation of polyurethane type inflatable boat glues. However, it is EXTREMELY aggressive...this is the key, since it chemically abrades the PVC. It is a vital step to the gluing process.
With that being said, Pennel & Flipo actually recommends MEK for bonding their ORCA csm/hypalon material.
I would get both.
If I had to choose though, I'd get MEK.
Gluing geek since 2007