It is fun to see the comparison between the 2. My eye is drawn to the first image (your second version). I think it is because the thicker book cover and I like how the bookmark touches the invisible surface beneath.
To be honest, I like the first image better because it appears to have fewer pages. I am not an avid reader, so large books scare me a bit.
RE: CG original study art - book cube (second version:)