Gyro vs. Encoders for Driving Straight

[beijing_strbow]

At the moment, our algorithm for driving straight doesn't work too well. We just start at a set speed and increment the left and right speeds by a small amount based on encoder readings. We get about 3-5 inches drift on an 80 inch drive, which isn't good enough (like this year, to drive to a position to shoot).

We're looking at implementing PID with either the encoders or the navX MXP, so which works better? I would think the gyro would be better, as there isn't drift from wheel slipping, and it also seems simpler to implement, but I read on a different thread that encoders are really the right sensor to use.

Additionally, is it worth doing a PID control with both encoders and gyro and averaging the outputs? Would that improve accuracy enough that it would be worth implementing?