http://openbci.com/forum/index.php?p=/discussion/155/compari...

https://en.wikipedia.org/wiki/Comparison_of_consumer_brain%E...

An excerpt from the forum post seems to point out that openbci uses the most advanced amp:

  Regarding data quality, I don't know of any other consumer
  grade equipment that has the research / commercial grade amp
  we are using, the TI ADS1299.  24 bit samples, programmable
  gain and sample rate, delta-sigma ADC design, sensor location
  flexibility, on-board programmability.  Much of the consumer gear
  has fixed 10-20 locations and only a few sensors, closed source approach, etc.