I use Strava, but it’s not brilliant, and it’s particularly good for editing once you’ve made the route, and can get very frustrating. Almost pointless for off road.
I’ve also been using getamap – the OS software – which works quite well, better for off road, but doesn’t snap to the roads or anything fancy like that.
GPSies also works fine if you get the route right first time, but isn’t easy to edit afterwards.
Garmin Connect…pretty similar to the above.
All of them are a little bit slow and ponderous, I’m not aware of any that I could heartily recommend.