Exactly the same question I've been asking myself, and I think (I'm going to have to try it to see what it looks like) I'm going to go with the Damier Tango, long strap.
I'm just booking a return trip to Venice, in March, so want something that is hands free, but not a back pack, that will hold a small water bottle, purse, camera and book.
Hoping the Tango should just about do it.
Won't be getting the bag till day after Boxing day, as will be down in Dublin for the Brown Thomas sale!
Let me know what you finally decide!
Good luck!
K
xx