DTW has some good spots, they just built a new extension to Concourse A, with a good viewing area on the bridge. Also the parking deck is a good alternative- it gives you a clear view of the airfield. If you going to stay inside DTW- the Northwest terminal should be good enough. More information like aircraft movements on my Planespotting @ DTW page, http://fly.to/detroitmetro
Have a great time at DTW if you end up stopping by.