My vote is for Clasico, but here are some general comments on the themes:
The elementary icons are very polished and elegent. Definitely keep this.
The Clasico (as with the traditional Trisquel) theme blends the window border
with the top menubar and gives a unified look to the whole window. The only
issue I have found with this is that when several windows are open, sometimes
they appear mixed together due to all the gray.
I like the traditional window buttons (min/max/close) rather than the colored
buttons. I also think that Gnome specifies using buttons that don't depend
on just color but also shapes for those that are colorblind. We are not
creating themes for Gnome but just something to consider.
I like the rounded window borders of Oscuro and Claro.
