Which method of wireless tether uses the least amount of power? Bluetooth or Wifi? If I'm going to wireless tehter to my Android phone what method drains the battery the least? Wifi or Bluetooth?
I decided to look up some data, and my guess seems to be correct: http://nesl.ee.ucla.edu/fw/documents/reports/2007/PowerAnalysis.pdf 

According to the report, Bluetooth takes the least amount of energy.

However your 3G radio will probably take the most energy; maintaining a 3G connection without transferring any data is cheap, but once you start sending/receiving data, then it trumps even Wi-fi.


  WiFi radios have a high wakeup and
  connection maintenance energy, but low
  energy per bit transmission cost and
  high bandwidth. 
  
  Cellular radios have low connection
  maintenance energy, but high energy
  per bit transmission cost and low
  bandwidth.


Disclaimer: The study might only apply for the particular model that the device they use.