Jamelle Bouie has been pushing hard for Kaine, I'm still kind of eh but I may come around as I agree with him on many other elements of this (such as the importance of keeping major players like Elizabeth Warren and Sherrod Brown in the senate, and the idea that any VP pick doesn't move the needle that much).
Kinda like Julian Castro of the other conventional wisdom picks out there.
I don't think it's going to be Cory Booker, even though I like him.
I haven't come up with any non-conventional-wisdom picks that I think would be good choices. Mark Dayton isn't going to want to leave MN I don't think. He's also too old -- need someone young and vigorous in the VP slot. Everyone else I can think of is in the senate and should stay there.