They are all supercute models! I would consider the bag depending on what you need in terms of size and probably when you want to use it.
I love love love the Denim Valley because it is sooo darn cute, but I would never buy it as it is way to small for me to have any use. It also is more casual, so probably suited for certain occasions to wear.
The PM and the Diane have a similar vibe and I think you can‘t go wrong with either. The PM is a bit dressier stylewise in my opinion, but only a tad. I have only the PM from this bunch and I think it fits more than I initially thought, but rather thin stuff because of the inner compartments. I can fit a small umbrella, phone, cardholder, tissues, hand sanitizer and some bib and bobs like lipbalm etc.
Good look deciding!