LVDS Flex Cables - Optimizing Trace Layout for 10 GbE
I would go with option 1.

The fundamental goal of a differential pair is that any unintended signal which couples on to one wire in the pair also couples on to the other wire in the pair, and since the receiver subtracts the two signals, they cancel.  This works better the closer the two wires are coupled.

Another argument is the inductive loop.  For single ended signalling, you want every signal running over a ground plane to minimize the inductive loop between a signal and its return current.  For a differential signal, the (differential mode) return current flows through the other wire of the pair, rather than through ground - so by adding a ground wire between the two signal wires, you actually increase the size of the loop.