This page is written by a fairly well-known bike guru:
Singlespeed Bicycle Conversions by Sheldon Brown
He does say a multi-speed bike may be better for going the furthest with the least amount of effort. I would say perceived effort isn't necessarily the same as power output... but it probably doesn't matter.
He does say:
"You can really feel the difference! A singlespeed is noticeably quicker and easier to pedal than a multispeed bike in the same gain ratio."
Anyways, this has been a fun discussion. A good bike is a great way to get around. Any bike that allows you to not use a car is a good one in my opinion
