I don't think it matters. I'd select whichever flight's departure time is better for you and your travel patterns. My family tends to waste time on the day of departure when leaving on a long international flight. For that reason (and the 90 minutes less flight time), I'd probably select the DTW flight because it also would get me in at 5:25p assuming the connection is made. Others make a good point about alternatives if there's a misconnect... that's the only thing making me lean towards ATL.