[At the time of typing ]Google Maps provides the best all round performance for cycle routing. There are other sites that can provide you with a gpx file of your route or written directions or a saved copy of your route but only Google Maps can provide ALL of them. [Although you can only get all of them out of Google if you know the tricks (see above) and use third party software to convert the route to gpx file format].
Beyond this Google Maps is also very easy to use (once you have a little familiarity with it) and you can produce even quite complex routes very quickly.
Another big advantage of Google Maps is the ability to be able to switch to satellite view which gives you a much better idea of terrain. It is also very helpful in working out exactly what is going on at junctions and roundabouts, which might be confusing on the map.
My favourite feature is the little golden yellow chap in the controls that you can drag and drop onto the map. He then acts as a set of eyes at street level so you can see exactly what is there (or at least exactly what was there when the photos were taken). This is a great feature which allows you to pan around 360 degrees, zoom in and out and even travel along the road.