I actually have both and think I prefer the Galleria. The reasons why I prefer the galleria is because it had a closure, the shoulder strap is adjustable and comfortable from day 1. I also found that the galleria fits more comfortably with a coat. It may be worth trying them both on and see which one works best for you. Hope this helps a bit.
I think the Artsy MM is better looking IMO. There's just something about the Galleria that makes it look unattractive. The strap on the Artsy is horribly painful though, at least this has been my experience!