I lived in Sturgeon Bay for almost 20 years, depends on what trails you plan to ride but for the most part I would grade them fair to poor. Southern door has many plowed fields that rarely cover with snow. The Anhapee Trail is usually lots of fun to Algoma. Northern door is experiencing large tracts of land that are being sold off in smaller sizes to out of area residents. These new land owners are quick to shut down trail access for snowmobiles, meaning lots of ditch riding.
Some of my best riding was along the Green Bay shore line on the ice south of Sturgeon Bay. You can park and unload at Otumbwa Park in Sturgeon Bay, ride through Potowatami Park and jump on the Bay of Green Bay by Sherwood Point lighthouse. Very scenic ride, stay in between the ice shoves and shoreline for smoothest trek.
Stay clear of Peninsula Park, average speed is around 10-20 mph, lots of newbies on rentals. Saw a guy one time that had a broken leg in a cast and was trying to drive a snowmobile with his leg elevated. Of course I was behind him, he would not pull over to let me pass and in Peninsula Park there is a strict speed limit.
HH