Whatever is on sale, but, once again, that's dirt, where we don't have to worry about temperature.
Have also heard of issues with Silicon/DOT5.
When researching brake fluids, make sure you check the WET boiling point, as that is a more true number.
The dry boiling point is pretty much an unachievable number outside of the laboratory, unless you regularly replace all brake lines and components and flush the system.
