They are all fine, there is no "best" among them. It depends upon your preferences: do you like it flat, or do you like to climb mountain passes? The classification at Veloland should give you an idea of the character of the route.

Try to combine them to a round trip that suits your preferences. E.g., last year I did a round trip using Route 5 (mostly flat) and Route 9 (some moderate hills). Equally, one could combine 7, 1, and 2 (Jura, Rhône, Rhine).

Stefan