IMO ideally there should be no question at all at start of navigation.
If I am somewhere near the route (but not on the route) maybe after a break, I want to be guided back to the route as seamless as possible.
Whether this is “nearest point on route” or “nearest waypoint” isn’t too important. But not both.
Keep the start menu as simple as possible!
Some people seem to expect start as an option as well, so I would offer start and one other option.
nearest point on route
Despite the issues dicussed here I still prefer nearest point on route
Maybe onother option could be “nearest unvisited waypoint”.
So that after a break, you won’t be guided backwards, providet that the route is still in memory.