Regarding the favourite in this competition people have already to discuss about this before and according to the odds Manchester United is the first favourite and following them there is Tottenham and AS Roma as the 2nd favourite and 3rd favourite but there is no guarantee being an the favourite will became an the champion because we all know Europa League is full of suprised and previously i have seen some of strong clubs were beated by weak clubs
If we analyze the squad quality, Man United and Tottenham surely become the most favorite teams to win this competition. However, we must realize that the performance of these teams aren't stable, they are even struggling in middle of EPL table nowadays. If there is no improvement on their consistency, it won't be surprised if these teams can't reach the final. There are some other teams that look playing more consistent in early of this season, just take a look at Galatasaray, Besiktas, and Porto. IMO, these teams potentially to beat those favorite teams.
Why Roma management sacked Mourinho is a mystery to me. Mourinho is a very experienced young man. If the Roma management had prepared enough funds to buy players, and if they had taken the necessary steps to strengthen the squad, Mourinho would have been able to strengthen the Roma team. But Roma management had no interest in spending money. Even so, it cannot be said that Roma's performance under Mourinho has been poor.
Roma board fired Mourinho because Mourinho can't keep the good performance of AS Roma. Mourinho can't bring AS Roma in the top 4 (UCL zone). As far as I know, at that time AS Roma targeted to finish in UCL zone. Personally I agree that AS Roma didn't spend good amount of money to build their squad, Mourinho gets difficulty to compete with other big teams. However, it is true that Mourinho could give a trophy for AS Roma. It is wrong if AS Roma is totally a poor team under his management.
Reference: https://www.instagram.com/brfootball/p/C2Kiu-QIQAm/