We can't really argue which club is going to win the competition because Leverkusen and Liverpool have never met. I hope it will come true soon. Only if Leverkusen and Liverpool consistently win the game in the quarter-final.
That's gonna be the first time leverkusen to play against liverpool.
How you can be so sure? if Liverpool can lose against Manchester United, there's a chance Atalanta can beat Liverpool. If Leverkusen almost lose against Qarabag FK, West Ham might able pull an upset.

Most of the times Europa league is full of surprise, so predicting the final match or the champion is kinda hard. Probably Roma will become the champion in this season.

Exactly, not just European football or Europa League, football in general is full of surprises especially in such elimination stages where we will be thinking that the big team will always win.
A shocking defeat to Liverpool by Manchester United is something to be taking into consideration. No team is superior than others especially when it comes to Europa League or Champions League quarter finals.
Liverpool can be eliminated likewise Leverkusen too because West Ham and Atalanta are all doing great in their domestic leagues and will also be preparing to make history by seeing themselves play in the semifinals of the Europa League.
People are been too quick to judge based on paper; we know that based on domestic Leagues, Liverpool and Bayer Leverkusen are the two teams with the highest chance of winning this Europa League, but that should not rule other teams chance of winning the League because we have AC Milan too in the competition.