As I can't leave earlier than 5.30 (children) which is the best route: via Aylesbury/Leighton Buzzard/Dunstable or via M40/M25/M1? Bearing in mind that it's a fairly trafficated time to set off.
I would avoid the M25 north of the M40 in rush hour. Several miles of roadworks and 50 limits, which turn into crawling and stop/start traffic. No idea if the other route is any better.