What is Your Favourite Michigan Golf Resort

I have not played or stayed at many resorts in northern Michigan but I think you would like Shanty Creek.  They have 4 courses with the Legend and Cedar River both being outstanding & beautiful tracks.  Accommodations can range from a simple hotel room to a large condo, depending on the room you want.  All the courses are connected via resort shuttle so once you are there you can walk or shuttle to all the amenities.

It's a tough choice between Shanty Creek and Boyne Highlands. There are more great courses at the Highlands than at Shanty Creek (Ross Memorial, Heather, Art Hills, access to the Bay Harbor and Hidden River courses. Plus it's an easy drive into Harbor Springs and Petoskey. Shanty Creek is pretty isolated.
 

There are a lot of nice golf resorts in Northern MI.  IMO the best two are Treetops in Gaylord and Boyne (Highlands) with an edge to Boyne.  Pros and Cons of each:

Treetops

Pros

Nice set of courses at the resort and another 5-6 nice courses within 30-45 minute drive (Elk Ridge, Wilderness Valley, Garland, etc.  Also Forest Dunes is about an hour or so away)

Arguably the best teaching pro in the entire country in Ric Smith is the pro (and owner)

Courses are managed well and in good shape

Lots of elevation changes which makes for great views, especially in the fall

Threetops course is fun to play (Also used to be the site of the Par 3 challenge back in the 90s with Mickelson Trevino, etc. playing it)

Cons

Gaylord is kind of a boring town

Lodging isn't the best (not bad but just not 5 star)

The courses are all nice, but none of them are an "experience"

Boyne

Pros

11 courses to choose from including 27 holes at Bay Harbor

Can get great package deals ($100 per night for unlimited golf, breakfast, and room)

Lots of good tracks and variety (Heather, Arthur Hills, Hidden River, Donald Ross Memorial which is a reproduction of 18 of his most famous holes)

Bay Harbor is one of the best public tracks in the country and gives you that "wow" factor

There are some very nice accommodations,especially for groups where you can get cottages.

Other nice courses in the area to play (True North if you can get on and Belvedere in Charlevoix)

Lots of things to do in Petoskey and Harbor Springs like the casino, bars, restaurants, shopping, etc. and the area is really nice

Cons

The courses aren't all in one spot, Bay Harbor and Crooked Tree are 10 minutes West of town, Boyne Mountain is 20 min South of town, and Boyne Highlands is on the other side of the bay.  None of the drives are that far, but they're not all right on site.

Can get pretty backed up on weekends.

All in all they're both nice resorts, but if you're looking for something more than pure golf or are looking to take a longer trip Boyne wins hands down with the volume of courses, and the fact that the area of Harbor Springs and Petoskey are much nicer than Gaylord with a lot more to do in terms of non-golf activities.

I have toured the grounds of Boyne Highlands and I think that place would fit what your group wants.  The courses are on site (4) and very well regarded.  The little cities in the area (Harbor Springs, Boyne City, Petoskey) are really nice for an evening out.

Shanty Creek, Boyne and Treetops are the top 3 in the state. There is also Grand Traverse Resort with 3 courses including The Bear by Nicklaus. Another is Lakewood Shores in Oscoda. The resort is definitely less upscale than the others but the prices are good and 2 of the 3 courses are terrific, those being the British Links style Gailes and the Pine Valley style Blackshire. All of these are right on site. Oscoda itself is a small town with little to offer but the resort has a restaurant. It's owned by the Aldridge family who own Indianwood Country Club.