What do you look for when planning a new route?

Great comments below.

Would also like an indication of the speed of the route based on the average speed of cyclists using that route then give my estimated speed based on my average speed as compared to the general average. If you follow that.

I tend to use cycle.travel in the USA. Google Maps wants to put me on main roads. What I really want is maximum gravel roads and minimum busy roads.

Another vote for Komoot. I find it great for cycling in London - it plots a direct yet quiet route. E.g. last week I had to get from Waterloo to Stamford Hill and then back (for work) and it took me on a delightfully quiet route with very little traffic. 

Quieter roads (generally avoid A roads and dual carriageway) so look for National Cycle Network and use Cycle.travel website that specifically looks for quieter routes; Komoot (sync with the computer) and CycleStreets are useful as well..  Happy to take a longer route to avoid an unnecessary climb/descent (on a longer ride to save some energy).  Try and avoid larger towns, if possible, as lights, traffic etc slows you down.  Setting Komoot with Cycle Touring often identifies good cycle path shortcuts in towns.  A bit of Google streetview is often useful, especially to check out a bit of the route that may have busy/hazardous traffic.  Most importantly; the cafe/lunch stop!

I like to plot routes along OS 1:25,000 'yellow' roads with the minimum on 'orange' and next-to-zero on 'red' routes. I don't mind routes being longer. So, seeing the OS maps layer is essential in my opinion. Most others - Google is the worst - give no context information. I don't use Komoot at all as its a completely closed system that you can't access without an account.

I have an OS Maps subscription but for ease of use tend to plot in Garmin Connect with an OS Maps tab open so I can see the sort of roads I'm going along and make adjustments as necessary. I sometimes download basic routes from RideWithGPS or other ''open" sites and modify them, if I'm going somewhere I don't have a basic knowledge of. I hate loops and usually plot an A to B route and get the train home.

Hope that helps!

I use PlotARoute (pro edition 'cos it's like a tenner).
Manual route plotting is excellent, with different degrees of snap to route.
I've not used it to decide a route for me - I'd rather plot it myself.

I'm not here to sell it, but I would recommend it to anyone that plots their own routes.

What I'd really like, and haven't been able to find yet, is something that does a decent job of taking (a) a point I want to pass through, and (b) a distance I want to do, and then finds me appropriate circular routes.

When I plan routes.....even on unknown roads and in unknown to me areas.... I focus on low traffic roads B, C unclassifieds and keep A roads to a minimum. I also factor in a coffee/pub stop too if a 35+km ride. I also look to ride a loop /fig of 8 even on Gravel/mixed surface rides. As for Komoot...I gave up.... the routes it offered or allowed to be planned were pretty rubbish to be honest.... I use Plotaroute which also has O.S layer on the Pro version which works brill for Off road/Gravel routes. Plotaroute also allows for multiple download files for various GPS units and also a .pdf print out... Clearly for me the Komoot set up didn't work, however much I tried to get a result. I would however....import a gpx/tcx into the app/website and happily plot it as a "Tour", yet wouldn't allow me to plot as I wanted.... strange but there you go. I also check all the routes if on unknown roads and riding area via the .kml google earth download on Plotaroute..... hope that helps and not causing too much of a rethink

I like features on Komoot which show the road type and surface as it helps me to avoid A-roads where possible. Especially when planning longer routes with greater distance between the waypoints I set. 

Ian's nailed it with the 'local knowledge' comment. If I'm planning a one day ride I'll usually ask someone. 

My personaly routing choice of website is https://cycle.travel/ which I find dead easy to use. 

The really tricky bit in cycle route planning is finding out which are safe roads.

There are major roads which are quite useable for short distances, especially linking across, we have to cross the A46 near Stratford-upon-Avon for several of our journeys, and as there is a wide non-cycle lane white line edge, and separated turn areas, it is manageable. Nearby there are B roads we would not use. Similarly, there are country lanes that are so badly maintained that they are not useable. Typically we would not ride through fords, but many fords have footbridges that are useable.

Strava solves this problem with heat maps, you get a good idea of preferred cycling routes from them.

In other words, the app needs local knowledge to be a good planning app.

For a good route planner that exists, Plot-a-Route represents one of the better offerings around, though the interface is a bit obscure.