The 2014 Honda Civic Hybrid model is the mileage champ of the lineup. It now has EPA ratings of 44 mpg on both city and highway cycles, and it provides more boost than in pre-2012 form, from a larger 15-kilowatt (20-hp) electric motor
EPA ratings for most of the lineup are at 28 to 30 mpg in the city and up to 39 on the highway. And in most Civic models there's an Econ mode that allows a gentler throttle calibration, along with more conservative transmission and accessory settings, but in the Hybrid you might need to turn it off to better keep up with traffic on hilly stretches.
In real-world driving, from our observations, the Civic Hybrid is very impressive. Over nearly 400 miles of driving—leaving the car mostly in 'Econ' mode—we averaged more than 45 mpg. As for the other models, we managed to about match the EPA city number in mostly city driving.
The Civic Si, with its larger 2.4-liter engine and lower gear ratios, is the 'guzzler' of the Civic line. It's (surprisingly) significantly thirstier than a V-6 Accord, especially if you tend to do mostly highway driving.