Radiator fan swap question

My 02 Tundra recently suffered a cooling fan disentigration that damaged the radiator in the process. I have already replaced the radiator and am planning to swap to electric fans due to the $175 price of a stock replacement fan.

I have to add a temperature switch to operate the electric fans. Should I place the temp switch in the upper hose flowing from the engine, or the lower hose flowing back to the engine?

My thought is the upper hose, but not certain.