It's hard to give definitive answers - there are really many variables that will determine which is the best RTV rubber and polyurethane resin combination.
I'll go home (it's lunchtime at work here) and write out some types of rubbers to use and for which types of molds.
Because I'm here in Australia, the brand names I use may mean nothing to you or your supplier, so I'll give you some info on different types of rubber and their Shore-A strengths, as well as a rundown on the different types of resins and how they need to be handled with different types of molds.
Better yet, gimme your email address and I'll send you info and pictures if you like. A link to my email address is at the bottom of this posting.
Cheers
LeeTree