It really comes down to what you're more interested in learning. If you like hard surface modeling like cars, tanks and things the car dvd would be a great choice. If you're into characters like me the organic modeling and t-rex would also be a good choice.
It comes down to what you want to learn first.
The reason the organic and t-rex dvds are only 4 hours is because, at the time, they were made to be able to watch on a regular TV so we had to cap the time to about 4 and a half hours.
Kurt
I am enough of an artist to draw freely upon my imagination, knowledge is limited, imagination encircles the world. (Albert Einstein)
https://www.artstation.com/kurtb