2. the most expensive of them.
3. as big as. 
4. the biggest of them.
5. the most modern of them.
6. the oldest of them.
7. more economical.
8. the most economical of them.
9. as fast as.
10. the slowest.
11. the fastest of them.
12. least economical of them.

Tom's car is more expensive than John's but Carol's car is the most expensive of all.
Tom's car isn't bigger than Carol's car.
Carol's car is the biggest of all.
Carol's car is the most modern of all.
John's car is the oldest of all.
Tom's car is more economical than Carol's but John's is the most economical of all.
John's car isn't faster than Tom's.
It is slower than Tom's.
Carols car is the fastest of all but it is least economical of all.