How fun - it sounds like your two teen daughters are in for a wonderful surprise.
You will probably get a lot of differing opinions about flying vs driving. Here's mine - Unless you can fly Echo in the cabin, I wouldn't even consider flying. I tend to be anal about safety and I just don't have enough confidence in airline employees to ensure the safety of a beloved pet.
Driving on the other hand could also be difficult. I visit my daughter - 7 hour road trip several times a year. Tsali and my three yorkies load up in my mini cooper and off we go. Always in the car, Tsali is wearing his Aviator Harness. During the ride, if traffic is light, Tsali rides on my shoulder, if it is heavy, he is in his travel cage. I make it a point to stop often so that we can all stretch our legs, potty break (me and the yorkies) and get water and snacks.
With this said, I want to add that I have had Tsali since he was 3 months old and he has traveled all his life. Prior to making his first big trip, we harness trained and took multiple short trips. He has never ever been bothered with car rides. If you choose the car ride method, I would definitely get him an appropriately sized travel cage that you can secure with a seat-belt. You will need one anyway for trips to the vet. Get him comfortable riding in the car in the travel cage, lots of favorite treats will help.