They can't guess the best route, they mostly avoid highways and include bike paths. Still, they often choose the same route I would pick.

I use it for testing new routes--it's fast to drag the route onto a different street. Then I get the distance calculated immediately.

Try ridewithgps.com and click Search. You can enter a city or zipcode and see the posted routes near there. And try http://www.mapmyride.com/search.