Well, I did the canals and a bit of railway line up to Luton on Sunday and it was a really great ride.
The urban bit following Regent's Park Canal to the River Lea Navigation is a bit slow, but really interesting as you get a very different perspective of the city from the canal.
The River Lea navigation is much more picturesque than you'd imagine and it quickly empties you out into open countryside at Lea Valley Park.
I mostly followed NCN2 and then diverted onto NCN61, so the trail was quite well marked and easy to find even without GPS.
There are a few minor roads around Broxbourne and then you're quickly into Ware - which is again, very pretty. Hertford was entirely forgettable, then we joined the Cole Green way to Welwyn.
To be honest, the route beyond Welwyn was lovely, but I could quite happily have hopped on the train there and called it a day.
That said, the road riding from Welwyn to Luton was great, really lovely open countryside, easy navigation and no hassle from cars. It was almost a relief to have some climbing and descending after the relatively flat canals and railway line. Getting back to town from Luton is super easy and fast too - about half an hour and only £15 for a super off peak single.