Compare the Frequency Responses using Different Methods and Sampling Times 
References
Books
1) Katsuhiko Ogata - Discrete-Time Control Systems (Second Edition, Prentice Hall, 1995).
("Chapter 4: Disign of Discrete-Time Control Systems by Conventional Methods", pp. 174 - 182.)
2) M. Gopal - Digital Control and State Variable Methods (Second Edition, Tata McGraw-Hill, 2006).
("Chapter 2: Signal Processing in Digital Control", pp. 89 - 95, 105 - 108.)