The "ancient" grey one has thick tiles. All newer versions (grey, red and black-red-mixture) have thinner tiles.
You should stay away from the cheaper black and white versions from cube4You that have "HomeMade" prints inside. Their strings are to tight and they will always give you DNF's because they just don't stay flat.
I think only Rubiks.com still sells the "ancient" grey version, but you can just DIY with whatever tiles/string/picture combination you like