I have both and I love them to pieces! I will say that the Galliera PM is the most comfy on the shoulder because of the single strap and being so lightweight. However, if you like the option of having a handheld bag, the Palermo will give you that and also can hold all of your things in an organized fashion.
Galliera! I have it and love love love it! I don't have any problems getting in the bag. I actually leave her on my shoulder and can grab my wallet or whatever I need very easily. I can't think of one bad thing about this bag!