What coolant to use??

[Jonathan]

I was just wondering where it is best to put the rad. Between the pump in the reservoir, so it pumps the water through the rad before reaching the spindle, or between the spindle and reservoir

It does not make a difference. Since the flow rate is reasonably high, once the system has reached equilibrium the temperature of the water at any point in the system will be virtually the same...only a couple of degrees difference, if that.
What does make a significant difference is the length of the pipes (flow resistance), so if either system uses shorter pipes overall that's the one to go for.