Aston Villa and Nottingham Forest are also two Premier League teams among the favorites in this tournament.
Forest were the most favoured one according to bookies before the league phase draw started. But after it finished they've immediately gone down to the 6th favoured with 12.00 odds.
Aston Villa are at the top with 7.00 for now. But I must add that they've started the PL horrible... Currently one of the worst teams there. If they don't recover I won't think the same as bookies to tell the truth.
So far, Aston Villa has only managed to collect one point in the Premier League, and in my opinion, this will affect their chances of winning the Europa League trophy. Nottingham Forest performance is slightly better than Aston Villa, and if they continue to play consistently, they are more deserving of being favorites. AS Roma and Real Betis are also on the list of favorites, but AS Roma is more reliable in terms of experience.
On the other hand, even though some teams are performing poorly in their respective domestic competitions, honestly, that can't be a complete benchmark for measuring their strength in the Europa League. I mean, last season, Manchester United and Tottenham were nearly relegated from the Premier League, but both teams managed to become finalists in the Europa League. I think that could happen again.