i would recommend the 180 or 190. i wouldn't recommend 170 since as soon as it hit's 170 it'll be opening and trying to cool to 170. the ecu sees 170 as the cold/warm point. anything below 170 is in the cold range and adjusts fuel and timing enrichments. you'll be constantly switching from warm to cold start mode.

if it continues after replacing the thermostat try replacing the temp sensor.