I`d prefer a creator at 12, and a ruthless finisher at 13.
My 12 would have to be a clairvoyant reader of the game, someone with an excellent pass, able to hit his target off of either hand, plus he needs to be a good communicator. And although some might disagree here, his personality needs to dominate the 10`s slightly, since your 10`s eyes should be on the flight of the ball from 9, while your 12 has that split second longer to make the call. The 3 best for my money at 12 are definately Giteau, Jaunzion and D`Arcy. And Catt`s actually a pretty decent playmaker too. But for my money, Gits just has that extra little edge as a playmaker, being a former 10 who knows how to read the game and communicate just a tad better than the others.
At 13 you want the ruthless finisher. While your 12`s job is to make a metre of space for your 13 out of a millimetre, the 13`s got to be able to exploit the created space. So he needs the raw pace, acceleration, stepping skills and power. Plus he`s our main guy on defense, especially if you`re playing a rush- he needs to smash his opposite number with ball and all. The 2 current test standouts, beyond a doubt Mortlock and O`Driscoll. I`d give O`Driscoll the nod over the rest, due to his superior finishing ability.