Some things you may not be aware of on the dual sections of the A1, especially important when driving along with both lanes doing 60/70: There are pedestrian crossings. There are T junctions. The service station slip roads are incredibly short.
There are still some single lane sections but it is a reasonably good road now and it is getting better all the time.
I've never been that route, but from what I've seen on the map a lot of the A1 changes from dual carriageway to single lane and back again, particularly when you get by Leeds. From Darlington onwards though, it's all dual carriageway right up to Newcastle.
Working all round the country I use both roads regulary but M1 more as I live near Jn 25
A1 could be the more direct routedepending on where abouts in London you are travelling from but some patches of dual carriage way, speed cameras, roundabouts etc. heavy road works at Blythe island (just south of Doncaster)
M1 has severe road works from Jn 6 -9 and is always busy most of the way up but no fixed cameras.
A lot of the single carriageway areas are now dual carriageway.
The main problem with the A1/M1 (at least where I mostly use it in the Yorkshire area) is, as mentioned earlier, the fact that there are so many road entrances and exits for other vehicles entering often very fast traffic flows.
It's almost like living in a town on some stretches...:-)