I will go to D2R, because of the graphics.
The game / content is the same, but it looks so much better!
If they change the content too far away from LOD-classic, which will touch the LOD-experience to much (worst case is, if they do it like D3), then I will come back to the original from time to time, but only Single-Player PlugY. Classic Bnet I am already done... broken mule-system, bots, etc.
If they implement new content to a third game-mode or a third "modern-ladder", then there is no reason to come back to the Original. Hopefully I can play LOD-content with new graphics all the time in a "LOD-classic" game-mode.