There are so many variables here that to get something meaningful out they really need to be trimmed down a bit by making some assumptions.
First off, aerodynamic drag is far and away the biggest factor, but let's assume that you want to carry on using the same bike as you already have.
The next biggest power absorption factor will be hill climbing and acceleration, in which total weight (bike and rider) is the dominant factor. Anything that reduces weight will reduce power required, but the effect is modest. If you weigh 80kg (176lbs) and the bike weighs 20kg (44lbs), then knocking 5kg (11lbs) off the bike weight only makes about 5% reduction on hill climbing and acceleration power.
Rolling resistance is proportional to weight as well, but will only vary slightly so can be assumed to be pretty much the same for whatever motor/controller/battery you choose to use.
The above stuff is hard to change easily, apart from reducing weight, which is a good thing but won't make a dramatic difference on it's own.
As has already been mentioned, controller efficiency is high and won't vary much between brands or types.
Battery efficiency, in terms of weight per unit energy, is easily optimised. LiPo is top of the tree, LiFePO4 is next, followed by NiMH then lead acid at the bottom.
The biggest single factor that you can change for greater efficiency, assuming the same bike and rider, will be the motor set up. Hub motors will never give best efficiency, because they will often be working at an rpm and load that takes them well away from the peak efficiency part of their operating curve. Depending on the nature of your average journey, this could have a major impact. Running a hub motor relatively slowly, during acceleration or hill climbing, will drop the efficiency right down, it will only run close to peak when run at around 80 to 90% of it's maximum speed (see Justin's simulator graphs on www.ebike.ca for an illustration of this).
If your average journey involves running at speeds below this efficient band for long, or has a few hills to climb or stops and starts, then overall efficiency would be improved by running the motor through the gears. This would allow the motor to run at closer to it's most efficient RPM range for more of the time. The net benefit from this would probably be greater than the slightly greater loss from running through the bike drive chain.
Going for an efficient motor is the next thing to look for. Many are only around 75 to 80% efficient, for example. If you can increase motor average efficiency (by careful choice) from, say, 80% to 85% you will gain a significant benefit. The reduction in lost electrical power would be about 25%, a worthwhile gain, plus the motor will run cooler, giving a further gain. A cool motor will be more efficient than a hot motor, as internal resistance increases with temperature.
I suspect that a good quality RC motor, driving the bike through a decent drive chain with gears, might well be the most efficient system currently available for the sort of power you might need. LiPo batteries would give the best efficiency in terms of being the lightest for the energy. Battery voltage with such a set up would depend entirely on your choice of motor and gear ratio, but might not need to be above about 40 to 50V for the sort of power you need. There are others here with more experience than I of this type of system.
If you really must have a hub motor, then I'd take a look at some of the geared types if your journey includes stops, starts and hills. They will probably be a bit more efficient, as, if all else is equal, spinning a motor fast tends to be better than spinning one slowly. You get more power from increasing motor rpm, with only a small increase in losses.
Jeremy
Heck, my 20 ah ping only weighs 15 pounds, carrying two would be no sweat if 25 miles of range was too short.
