You guys keep talking about experience and all but you keep forgetting current form. As hard as it is for people to accept, Barcelona under Xavi is better than United under Ten Hag. Barcelona have managed to win all the top teams in La liga. They may be winning by small margins recently but they're are a very technical side. Xavi as well as Ten Hag is a tactical coach. He knows how to read games and make during-game tactics. If injuries don't happen to Barcelona like it happened before their UCL ties I think they win Manchester United.
If you look at past records and years spent in the managerial dugout you will get to see why people rate Ten Hag much higher than Xavi. Meanwhile Ten Hag has set up one of the best Manchester United side for the past five years but Xavi already spent a complete season at Barca and he is yet to get that consistency needed in the team. Although both coaches are excellent but Xavi isnt in the same bar with Ten Hag just yet.
Barcelona is on top form,they are leading comfortably the La Liga now after Real Madrid did not win yesterday night but what is important for the Europa League is the form of Barcelona which they have so far in La Liga conceded only 6 goals which is a really small amount of goals conceded.It shows a super solid defense by Barcelona and on the other hand Manchester United is not in that really good form recently and now that the encounter is coming Barcelona is clearly the most favored side by the bookies and everyone else.I don't exclude a Manchester United win though as English teams are well known for that,to surprise everyone.
Both teams are currently amongst the most inform teams in Europe top five league. The most interesting thing about this match is what you just stated in which is the defense. Both clubs have been keeping lots of clean sheet this season with both Ter Stegen and De Gea high up in the clean sheet standings. But united will be going into the the match without there best center back pairing of Varane and Martinez, since Martinez will be missing out on suspension but the recent form of lindelof and the successful experiment of Shaw at that role will provide Ten Hag with options