Best sensor for measuring rotation angle?
Rotary encoder  
Optical Encoder 
Discrete hall effects at predefined positions (viable if you only need zonal info - BLDC) 
Linear hall effect sensors either 2off at quadrature &amp; use atan2( via cordic), or 3off at 120deg displacement and use park&amp;clark.
resolver


I would say for your requirement two optical encoders slightly displaced from one another to increase the angular resolution