A1 for us but we are close to it and went up to the East coast Dunbar in June at that time there where no road works and it was a smooth tow all the way up with no round abouts ti over the border.just under 7 hours to cover 310 miles including to rest breaks.
It all depends on how far your going into scotland. Your on the boarder of going one way or the other. I don't think there will be many miles in it. If it was me i would go M1/A1/A66/M6. only for the reason that the holiday traffic will be mayhem on the M6 lower down. + there's better views.
For anyone considering using the A66 here is a quote which may make you reconsider. "The middle section of the A66 between Scotch Corner on the A1 and Penrith on the M6 forms one of the key trans-Pennine trunk routes and has one of the worst road safety records in the UK." For this reason use the M6. I now live in Perth in Scotland and previously lived in Hampshire. I travel the M74/A74/M6 route every year and usually 2-3 times per year without incident and not too many serious delays. Choose your travel time to avoid peak travel. I also have TOMTOM GO750 SATNAV which lets me know of traffic delays and whether to use the M6 Toll further south or even a re-route in times of road accident/closure anywhere along route.
A66 between Scotch Corner and Penrith and also on to Keswick is now a first class road as long as the wind is not too bad.
The section through Bowes Moore hosts Englands highest Hotel which you will drive past,it is very exposed so you can imagine what the wind can do up there.
You're in the east, you're going to the west, and the M6 runs north/south so you need to get across country and the A66 is the natural route. Yes it's pretty high over the top but it's now a far better road than it used to be with several new stretches of dual-carriageway and importantly, it's dualled over the high section.
So M1/A1/A66/M6/M74. You then have the choice of either A70/B742, or A71/A719/B742. Annbank's about 20 minutes from me!
We go up to Scotland every other year for many many years so have tried different routes. The best for us is up the A1 to Scotch Corner then onto the A66 - M6 - M74. We've tried the M1 - M6 a few times but every time we've just sat there and wasted many hours. We don't seem to encounter much traffic if we use the A1 - A66 - M6 - M74 route.
I 1st went to Scotland in 1980 which probably shows my age somewhat