Tom, who is considering purchasing a new car, is comparing fuel efficiency between models by car-maker C1 and car-maker C2.

Answer: Car-maker C1
Explanation:
The minimum value is visually shown as the tip of the left whisker. For car-maker C1, the min value is 12. For car-maker C2, the min value is 10, which we can see is less than C1's value. So that's why C1 is the answer.