The only time I use a mold release is when I'm casting RTV against RTV or resin against resin. If you are asking what to use when making the mold, what to put onto the part so it will come free of the rubber, in the case of silicone RTV you don't need a mold release. If you are using a urethane RTV, I can't advise.
If you are casting urethane resin into a silicone mold, no release is necessary. I know that's going to go against what a lot of people say here, but I've been casting urethane for over 15 years and have yet to find it necessary to use a release. Save your money.
When casting RTV against RTV, just use Vaseline. Brush on a very light coat no more than 5 minutes before pouring and the two halves will come apart with no resistance.
If you are going to cast a resin against resin, first apply wax and buff it out so it shines. Resin won't stick to resin anyway, but this makes separating the parts easier.
Scott
CaptCBoard@AOL.com