I love them both so much! I have the Neverfull Damier mm and I'm totally in love with mine, I want to use it every day! But I love the Trevi as well, I don't have it but I think that will be my next purchase! Good luck, that's not an easy one!
The trevi is a beautiful bag so it's a really tough choice; however, since the trevi is on my wishlist, I would say get that. I tried the trevi on in the store and even if you fill it to the brim, the attached strap is very comfortable. Definitely a great bag