I would go for the northern route. For petrol use the Sainsbury's at London Colney(adjacent to J22) rather than services. Certainly take a comfort break at South Mimms services or Sainsbury's as you could be spending a long time in the car afterwards.

Selective widening means that the M25 isn't as bad as it was 8 or 9 years ago, you should get round without using the parking brake these days. If the roadworks are still in place between J25 and J27 you may find it better to go A120/A10 to J25 rather than down the M11.

Certainly avoid the M4 in the evening rush hour, last time I went that way it was stop-start to Swindon.