Leverkusen definitely looks to be the best one and I believe we are going to end up with a much better return without a doubt. I think it's clear that we are going to end up with a result that won't be all that simple, we are going to end up with something that's going to be a tough game for both sides but Leverkusen looks to be the better team this season, well to be fair last season too.
Dortmund isn't bad, I do not mean to say that they are bad in any way, they are good of course, and I believe they are going to finish higher than where they are right now, I think a top four is still possible for them, not saying likely, but possible. However, Leverkusen is just better, and that's why I believe they are going to win that one. It looks like Leverkusen had a bad start to the season which does happen to many teams, but they did manage to figure out a way to get back on their feet and now they are doing better for a while and they could even fight for a title, very difficult of course, but not impossible.
You are right, Leverkusen had a bad performance from the beginning of the season but now they are playing well to the extent that they have a close gap between them and Bayern Munich, Bayern Munich was leading the table of the league with 9 points but after losing and drew some games their points reduce and Leverkusen use that opportunity to play well and win their matches and close the gap between them, Bayern Munich is still leading in the table of the league but before the season we are going to see a surprise result.
The reason for the improvement in Leverkusen's performance could be attributed to the number of games they have played and the challenges they have faced althrough this season and how much errors they made during those matches most especially how much they have managed to improve on all of these errors, I think all these and many more have helped shaped the team and probably made them appear to be a better side than Bayern Munich perhaps they might overtake Bayern Munich to the top by January or Munich might fix their loopholes and resist from giving up their position by improving more on their performance.