The hotter the engine runs without overheating the more efficient it becomes and the more power it makes.  I've always run a 180 t-stat in my '67, and a 195 in my '89 GT and other Fox era cars.  The thermostat is to set the temperature at which the engine should operate.  Ideally this would be 195 or more.

Fan on temperature is set based on where it needs to be set to keep the engine at that temperature or slightly above reliably.  There are OEM applications where the fans don't come on (unless the AC is turned on) until the coolant hits 225.  I have mine set to come on at 195 in my '67.  This combination yields an engine I've never seen run above 210 degrees even on the hottest, most humid day I've driven the car (heat index well above 100, actual temp above 98).

If both are set at the same temp you can get a situation where the t-stat opens, the fan kicks on and the coolant temp drops too fast causing the t-stat to close, and it gets stuck in a loop like that, hitting operating temp, dramatically cooling down, and so on.  It's really only likely an issue in cooler weather, but its annoying when you see it. 

I'm a fan (heh) of doing what works.  Your current setup, provided the gauge is accurate, isn't working.  I don't think the issue is the t-stat or fan on temp setting. 

So I have a 210/195 and a 185/175 switch...The thermostat is 180.

The fan would come on at the higher temperature and turn off at the lower temperature.  I didn't like the higher switch because the fan would come on when the switch read 210 but the engine temp was closer to 215-220.  Which from what I understand is normal for 5.0 engine but I don't want  to risk any overheating issues.

Which switch should I use?

I have two fans, They are controlled by Revotec adjustable controller. I set them upp to 87-90c. If one fan doenst lower the temp enough the other kicks in. Before I controlled them with the sniper unit.