My favorite is probably my ebene Berkeley because it's like a Speedy but a little dressier and with more structure to it, but I probably get the most use out of Batignole Horizontal. Whenever I take the BH out of it's dustbag I realize how much I've missed her and think to myself how I should take better care of her. She is truly my workhorse bag!
I rotate through all of my bags based upon my outfit or mood. Only my smaller pieces are saved for evenings, and my messenger bags are saved for days when I want to be hands-free, like when I'm Mall shopping or at the movies with my kids.
My Trevi is my most used bag since I bring it to work... on weekends if I'm wearing runners, I'll switch to my Papillon or Eva... dressier weekends I'll use my Artsy MM.