No real preference. I might prefer decent quality foam simply because cork pits.

I slightly prefer a good foam grip.  They seem to be more durable when abused and require a little less maintenance.  Though, I own cork grips too, and as long as they're quality cork, they're fine by me.  

I would like to try graphite.

I am full cork guy, But sometimes you don't have that option, Like my 908 Dobyns champion, or my spinning Conquest 842 that split cork handle.

I really don't know why but I feel much better using full cork handles.