What is best hybrid mpg?

I would have to give that title to the Toyota Prius.

Though there are other excellent hybrids on the market, it's hard to beat.

Upgrades like a cold air intake, and Pulstar brand sparkplugs are also good ways to increase efficiency in many vehicles.

The best I have heard is the Prius with an after market plug in battery kit and engine cut off switch. with an average 30 mile PHX area commute he gets around 100+mpg. This works by charging the auxilary battery at night and shutting off the gas engine at speeds below approx. 45mph. To get around the origonal computor they have to leave the origonal prius battery. Then they add another battery that is charged at home. This second battery trickle charges the factory battery so the computor thinks the gas motor does not need to come on to charge the battery. This also voids the warranty.The engine cut off switch prevents the gas motor from turning on when accelerating from a stop. This could not be done easily with the early models and the early ones also had a smaller electric motor.
---The Prius is also the best I know of un-modified. An aquaintance lives in indio, commutes to LA and averages 50mpg.