Hey Frank,
I'm using a 160 degree stant from NAPA with 2 1/8 drilled holes on the sides. They are one of the best to get. DO NOT, and I can't stress this enough, buy a mr. gasket thermostat or any of those out of advance or autozone's performance section. My father and I both tried them and I barely had 10k miles and my temp climbed to 225 at one point.
Now you gotta figure what part of the country your in. I'm using a 160 with a flex fan and s-blade electric fan on a switch because I'm in south texas where we get decent winters and hot summers. My motor stays at 170 on a nice day cruising on the highway. Since your in Michigan, and I don't know if you drive yours everyday during all seasons, I would suggest sticking with a 180 which helps your motor heat up faster during cold starts and giving you warmer air. Are you still running the heater in your car?