The little pliers
Among the various types of pliers on the market, small pliers are the most common and easiest to find. They can be sharp, for pinching sleeves, opening broken rings or unhooking fish.
Cutting pliers are especially useful in tricky situations, such as when you need to remove a hook that's set too deep without causing damage. Sleeve pliers are specially designed for this function, and are very useful if you use sleeves, but can only be used for that purpose. The most important pliers to have are the barbed pliers, whose jaws end in a pin. They are multi-functional, so they can also unhook fish or crush barbs, although they are not designed for this purpose. You can also opt for a disgorger with long, slender jaws that allow you to go deeper to unhook a fish that has become engorged.

Pistol grippers
Pistol pliers are specially designed for retrieving lures or hooks in places where you can't put your fingers. They are mainly used for pike, whose teeth are unforgiving and where it's best to avoid bringing your hand too close. They are also very practical at sea, as most big fish also have nice teeth, but are especially dangerous when they shake their heads with hooks wandering around.
Two different models are available, one with a small, classic jaw that closes when the handle is pressed, the other with a hook that allows the hook to be gripped and locked in a notch. The jaw is very practical for fine hooks and freshwater, while the hook is more suited to large hooks and the sea.

The big pliers
When it comes to strong fishing or big fish, the classic small pliers of our everyday fishing are not enough. This is easy to see as the lever arm is much smaller, reducing the force you can apply. The XXL version of the broken ring pliers also features a lug, which is obviously much larger and holds the rings in place much better.
Most models also feature a cutting zone on the top of the pliers, making it easy to cut braid and fluorocarbon. Beware, however, that these are not true cutting pliers: hard materials can easily damage the cutting edge.