The best PC controller is not always the keyboard and mouse. There are many titles that are best enjoyed with a gamepad. PC controllers can give you more freedom of movement and allow you to assume a more relaxed and comfortable position and more precise control in certain games.
Apart from the eternal debate concerning symmetrical vs asymmetrical analog sticks, we cannot deny that the Sony DualShock 4 is as functional as possible: it features an excellent D-pad solid buttons, a touchpad, motion sensors, wired and wireless connections while maintaining a very reasonable price. It just lacks some autonomy and is otherwise a great gamepad.