Buick Centry 油耗和日本车的差距很大, My Centry can do 6.9L/100Km on HW and with AC on, and 8.8 L/100Km local,
For Camry V6 or Accord V6, that value is 11 L/100Km HW and 14L/100Km Local with AC OFF. and even worth for I4 engine if AC is on, especially for Camry. Toyota cars are not power enough to drive the AirConditionor, if AC is ON, the engine is working out of it's normal range.
If you considering gas usage issue, forget Nissan, Altima may be very good on gas, but it also can exhaust 20L/100Km, sometimes the value can be as lower as 10L/100Km, this can happen with the same driver the same car, the same road condition.
Jap cars just burn gas for no reason.