if you fly into ORd you can take the train in, but it lets out in town pretty far from Mag Mile, so you have another taxi ride. If you're taking a taxi (or Uber, my preference), ORD is a bit farther from mag Mile (16 miles versus 13). Cost by taxi and time getting into town from either really depends on how bad the traffic is, and either can be pretty bad. Est. cost $30-50 usually

IMO, really depends when/why you need to get to Mag Mile.  And secondly, where you're coming from. As someone said, neither is ideal, but I usually recommend MDW for my clients if they can get a good flight into there.  

And a big SECOND on using Uber.

Hop on the Orange line at Midway, transfer to the Red Line at Roosevelt and get off at either Grand A e or Chicago Ave. depending on where our hotel is.  You're a block from Michigan Ave. at either of these stops.  I think the care is $2.50 and it takes about 35 minutes.

Both are served by the L. Midway is the orange line and it has fewer stops than the blue, which serves O'Hare. Hop on the orange line, ride to Roosevelt, walk downstairs and then east to Michigan Ave, hail a cab or Uber and it's just a short ride north.

Both services now can pick you up at the airport.....
Cheaper than a taxi....

Ride On!