This season the Europa League is difficult to predict because there are many great teams in it. Some of the teams you mentioned are teams that are not weak in their respective local leagues, so there are many possibilities that could happen in the Europa League this season even though the ones that are most often discussed are Manchester United and Fc Barcelona. But they both could have been knocked out by some of the teams you name in the Europa League this season.
The match between Manchester United and Barcelona is the most interesting to look forward to, because both teams are regulars in the Champions League, but this season they have to go down in caste. Manchester United were unable to finish in the top 5 last season in the league so they were forced to play in the Europa League, while Barcelona surprisingly had to be eliminated because they lost on points to Bayern Munich and Inter Milan in the group stage.
Manchester United qualified for the knockout phase of the Europa League as runners-up, so at the time the draw was made Barcelona came out as their challenger. There are many predictions that people make that Barcelona's chances are bigger than Manchester United, but I have faith that Manchester United can overcome that at Old Trafford.