I differ a bit R1 bhai
OHV = push rod engine = valves open close thru a push rod system = inaccurate valve timing at high rpm = more vibration
OHC/SOHC = timing chain engine = accurate valve timing comparatively = better mileage, better power = lower vibrations
DOHC = dual timing chains = supports multiple valves per cylinder = highest compression = most fuel efficient = less vibration = most powerful
EG: Honda City = 4valves per cylinder, great mileage and power. vvti, v-tec etc are again technologies and engine designs for better and better valve timing thus saving fuel and adding power...
Its all about how fully u can burn the fuel and get most power out of each and every drop