In terms of millage, I don't think it makes much difference.
In terms of freeway tolls, The southern rout is a toll road as I recall.
NOTE: if you take the toll road, you can go all the way to around Elkhart and then cut north to South Haven.
But From ELkhart to Detroit, I headed straight north, picked up some roads I know and I-94 south of Battle Creek (Lakewood) and then East.
That was the day they raised the toll you see.
NOTE: Odds are good you will hit construction on I-94, check with www.michigan.gov/mdot