All of the off-site parking at DTW is in the same general vicinity (north of I-94 on or around Merriman Road). They all seem to have frequent shuttles to all three terminals. Qwik Park calculates hourly and is up to 9.50 per day and $55 per week. US Park is also hourly and is up to 9.25 per day and $55 per week. Park-N-Go is $7.50 per day. My family has used a couple of those lots in past years, but I can't recall which ones. I believe that most, if not all, of the off-site lots offer coupons on their websites.
It is kind of odd that the Big Blue Deck is less expensive than the off-site lots. I've used it for my last two flights out of Metro. Parking in it is convenient for the Smith and Berry terminals, but not so great for the McNamara terminal. The main thing to remember with the BBD is that the Smith terminal is at the south end of the deck, shuttles pick up and drop off in specific locations on the first and third floors, and just because there's a sign saying "elevator out of order" it doesn't necessarily mean that both elevators in that bank are out of order. That last point was kind of frustrating last month!
The biggest benefit of the off-site lots is the shuttles. The drivers usually watch where you park so they can pick you up immediately and will wait until you're in your car with the engine running before they consider you officially dropped off. I think it all comes down to cost savings vs. better shuttles.
