What is the best way to power the MBP. Should it always be plugged into a power source, or should the battery be continuously being drained, etc. I've heard of arguement from both sides, so anyone know for sure?
There is no argument, only fact and fiction. Two types of usage that will degrade your battery faster are: leaving it plugged in all of the time with the battery kept fully charged and frequent deep discharges (discharging your battery to zero).
Use your battery at least once a month to keep it healthy. Charge it when convenient and keep your computer as close to room temperature as possible. Temperature extremes are unhealthy for the battery and will also degrade it faster.
Take a look and http://www.batteryuniversity.com for lots of good, easy-to-read information on batteries of various types, including lithium ion types.
Inherently all batteries will degrade over time. I don't see any harm in leaving your laptop plugged in for most of the time. It would be in your best interests to calibrate your battery regularly and use the computer solely on battery power. I can't see babying a battery extending its life, i.e. years, by some gross amount over not babying it.
Babying your battery, as Gymnut put it, is acceptable and all but how much battery life will you really save? If you ask most MB/MBP (or any laptop) users they will tell you they leave it plugged in most of the time and they are a-okay. Battery technologies have come a long, long way. Try powering a current laptop with an older battery lolz. You'd need a gasoline power generator. They're made to last and, unless defective, they do just that.