Depends on the car. Small sports cars (ie: Miata, Z3, and Elisa) should be measured in skid pad. Larger sports cars (ie: Corvette, Ferrari F355, Porsche 911) should be 0-100-0. Muscle cars 1/4 mile easy (that's what they do). Trucks, peak torque. Economy cars, sticker price. Supercars, top speed. Family cars, 0-60.
Engine displacement and specific output are (IMO) poor measures of a car and rarely result in meaningful information. When an Integra loses a 1/4 mile race to a Camero is he gonna scream out his window "well my engine makes more HP/L"? (god, I hope not). Or conversely, when a Camero loses to a 911, is he gonna scream out his window "well my engine is bigger"?
Personally, I go for things that cannot be measured. Feel and chassis dynamics are a big thing for me. Under hard acceleration does the car have a nice "squat and launch" feel or a "tip toe" feel? On entry into a corner, does the front feel like it's planting down hard or trying to pull up? And what is the rear end doing during this? Does the engine suit me personally? All subjective with no conclusive right and wrong answers.