Use the stock thermal paste that comes pre-applied. Later, if you should have to remove the cooler at some point, THEN clean off the pre-applied TIM (Thermal interface material) and apply the MX-4 or whatever product you prefer. The MX-4 is pretty good. I like the Thermal grizzly Kryonaut a little better myself, but I have both on hand. For starting out though, there's really no compelling reason to not use what comes on it out of the box.