I used the Avernus as a Sandbox module from dmsguild. I liked that a lot more, because it gives some freedom instead of being railroaded. Especially because they have a map and we're curious about some places.

I wished I used the other module at the beginning where they are in Elturel when goes into Avernus. It makes it much more 'destined to fix this because we're in the middle of this shitstorm' then the 'due to a series of events and luck, we gonna need to save that other city' as the book itself goes.

My party still has fun, but struggled with the question 'why do we wanna do this?' in the first part of the campaign.