I have no final answer, but I will try my best
In my experience, there are different points to "calculate" the stress for a rabbit.
First of all, I want to mention the point of companions: A lonely rabbit would not resist stress as good as two or more well bonded rabbits. They would find comfort in the other rabbit, which no human can give them. (In nature rabbits share the task to look for dangers, while the other rabbit can take a rest)
Second is the character of the rabbits: For example I have one, very sensible reacting onto sounds. So I would assume, that for him a long silent trip would be less stressfull than a short loud one (ie in an airplane).
The next point are breaks: My rabbits would prefer a trip, which allows them to have breaks with possibility to move and eat. When driving 1400km last weekend we had breaks every 3 hours, one over night in a pet-friendly-hotel. The short breaks were done as follows: We stopped, took the exercise pen onto the next clean green grass and put the carrier with open door inside. We had a blanket with us, to cover one side of the pen, so the rabbits felt more save inside. Then we were going one by one to toilet, eating, taking fuel and so on. The first out and the last in on each break were the rabbits (and the child ^^). The long break at the hotel the rabbit carrier was placed in the shower-tub of the bathroom and the rabbits were allowed to roam there the whole night. We put old blankets/towels into the corners (where they most probable want to urinate) and cleaned all in the morning.
I have thought about flying with them too, but for me it was no option to let the rabbits fly in the luggage-part of the airplane. There it is very noisy, and this is no option. I heard about some vets, who give the pets a sedativum before the flight, but I have no experience or knowledge with this in rabbits. Sadly the hand luggage was not an option too, because the airlines in my case did accept pets only in carriers, which were too small to fullfill the minimal needed measurements for rabbits to sit upright, lay comfortable and be able to turn around.
As additional point: For us it was more easy to first move (furniture by truck, people by plane) and let the rabbits stay by friends in this time. Later we took them and our car to our new home.
And something important in general: rabbits react with health changes when stressed. So stress makes them literally ill. You can help them with immune-supporting treatment some days before and after the stress (ie moving). (For us alfavet RodiCare Immun worked very well, dropped into a small amount of mash each evening, 4 days before and 4 days after moving)
