Implementing digital controllers on low-bit microprocessors has always been an attractive way to reduce costs. For that, this paper compares the eight common kinds of digital controller realization forms in terms of coefficient sensitivities, aiming to find better ones. 1D and 4D forms are ruled out for low signal-to-noise ratio. Two indexes, sensitivity of poles and zeros(SPZ) and sensitivity of gain(SG), are introduced to describe the average drift of poles and zeros, and the sensitivity of gain, respectively. It reveals that the cascade of 2D/3D's poles and zeros are less sensitive to coefficients than the parallel of 2D/3D's; therefore, the cascade of 2D/3D is recommended among the eight studied forms. Relevant analysis and simulations are conducted to verify the conclusion.