I've cast with meehanite cast iron molds, steel molds, brass molds and aluminum molds.
When money is no object, I find meehanite cast iron molds to be my favorite. The material seems to be the best at maintaining it's temperature and the they are simply a joy to cast with.
That said, I've never found the material the mold is made from the affect accuracy. And you simply can't beat the value of a Lee six cavity mold. I've yet to find a Lee handgun bullet design that didn't shoot very well, I just haven't tried their rifle molds yet.
Aluminum does require a bit of care as it's the softest material used for molds, use a bit of lube on the sprue plate to keep it from galling and don't slam the mold faces together. You should be able to produce 10's of thousands of bullets from a lee mold.
