Eric.
There is nothing like the BEST, only the best suited application z or y.
RTV rubber and Silicone have different properties and thus are suited for different applications.
Rather than worrying about the mold material, have you considered the following:
1.) Parts per mold
2.) Layout per mold
3.) Which resin will be needed for the best casting result(curing times)
The above will be affected by how your casting method: manual, spinning, rotor, vacuum, etc.
Either way I would order about 3~4 times the expected amount initially. as you will need a few tries before the molds are correct(no trapped air, good pouring channels, etc).