The most scenic part of US 2 is from the bridge to Escanaba, so I would suggest M28 then. M28 is a great drive along the Lake Superior shoreline from Munising to Marquette. Other than that stretch, M28 is not a very exciting drive.
If you do decide to take M28, make sure to stop in Munising and visit some of the waterfalls, especially Olson Memorial Falls and the nearby Munising Falls (no cache there b/c it is in the national lakeshore).
Between Marquette and Munising here is a virtual that has been described as one of the most interesting virtuals in the state Lakenenland
Also, in Marquette, you should take a ride up to Presque Isle Park (KAWBAWGAM cache)
Here is a bookmark list of caches that we keep for excellent UP caches Can't Miss UP Caches bookmark list