Horsepower with mileage options

He is looking to get into the low 20's mpg, 95% of the driving is done in town driving currently. He doesn't have concerns on 1/4 mile timeslips, just good light to light power. Well and being able to beat my other son's powerstroke diesel, which is no easy feat.
City milage is tough. Smaller engines have the natural advantage when idling.