Definitely Pomme. I think all of the bags can be dressed up & down. I've seen pictures of the Pomme Alma in celebrities section dressed down. I saw a Rose Pop Alma at the airport very dressed down. The woman was not dressed trendy, but she looked very nice.
Can't go wrong with the Alma and SD; I have both. I do not like the Bellevue - it's an inconvenient shape and I can see elbow/arm indentations on this bag in the future like on the Houston. Depends how you are going to carry the bag and I don't have time for those worries when it comes to my bags. Let us know what you decide!