I think not really have problem between Manchester United or Atletico Madrid because both team still not safety on 4th standing position on each domestic league, I see have potential for Manchester United will qualify next round with playing home on second leg. But some time Manchester United is not always take advantage playing as home because many time loss three points when play on Old Trafford. I think second leg match of EUFA Champion League will be interested match for both team and who pass to next stage.
At the moment, both teams are losing the fight for 4th place in their home championships. As for the return match, I certainly hope for United, but I think that the result will be as random as in the first meeting - both teams are in crisis and if one has a "good" day and the other does not, then we will see one result, and if the other way around opposite. It's impossible to predict anything here.