The record of the previous meeting is actually not too important in the upcoming match, but usually the team that is dominant in winning the match is the one who wins it the most. So I think Barcelona are the favorites in that match based on their head-to-head record, but I don't think Barcelona can be completely relied on in Europe this season after they failed in the Champions League.
This season, Barcelona has had pretty good results in La-Liga, despite difficulties in European competition. However, MU position is worse, both in Europe and in the EPL (now look like better). This is then makes me believe if Barcelona has a better chance of winning than MU in the upcoming match. H2H is superior to Barcelona, but that's not what I see, but the current performance. However, an H2H that is not matched by the current good form will be history.