Class rundown

Fighters and Bruisers are synonymous - bulky damage dealers. Depending on the context, Bruisers tend to lean towards the Juggernaut side of the definition and the term "Bruiser" is incredibly outdated.

Fighters as a whole are damage based champions that need to supplement their playstyles with a balanced defense. As a class, they differentiate from other damage based classes like Marksmen and Slayers, and are functionally different from Utility based classes like Tanks. They tend to be entirely melee, meaning they don't have the mechanical advantage/defense that a Marksmen's range offers. They lack "active" defensive abilities like Fiora's Parry, Yasuo's Wind Wall, or the high mobility of Assassins like Zed, meaning that they must rely on Passive defenses to survive, such as building some defensive items. It's important to realize that Fighters are a type of Carry class. This is what separates Jarvan from Maokai; Maokai will initiate a fight, lay down a lot of CC, and maybe do some damage as a side effect. Jarvan will initiate a fight, lay down some CC, and blow up a squishy champion if he's not properly dealt with.

Fighters are broken into two subclasses, Dive Fighters and Juggernauts.

• Dive Fighters tend to be the middleground between Tanks and Assassins; they're huge threats to squishies, highly mobile, often come with weaker but more flexible engage tools, but lack Active defenses so they need to build Tanky depending on the situation. Examples of Dive Fighters are Jarvan, Lee Sin, Vi, and Camille. You should notice these champions can pack a punch but they never build full Damage like an Assassin, and that they're pretty bulky, but nowhere near that of a Tank nor the CC and Utility a real Tank can offer.
• Juggernauts on the other hand are the more "Carry" side of the Fighter subclass. They relate more to Marksman and Skirmishers in that the only reason why you're picking a Juggernaut is to be a major damage presence for the team. Like Slayers and Marksmen, Juggernauts are more indiscriminate with who they kill; Dive Fighters aren't normally optimized to kill other Tanky champions for example, whereas a Juggernaut will tear through anything they can get in their hands. However, many Juggernauts lack inherit defenses like a Marksman's Range or a Skirmisher's Active defenses, meaning the only way a Juggernaut can survive long enough to bring the pain is to tank through the damage. Examples include Darius and Illaoi, as well as many "proto" Juggernauts like Nasus and Volibear.

Do realize however if we're talking about Top Lane as a whole, almost every subclass has a champion that goes Top, so technically speaking you're asking for an explanation of every subclass.

what u need this info for. they all trash anyway

diver = gapcloser with cc and some tankiness. j4? bruiser = 1 damage item, rest tank. darius? fighter = builds damage, 1 def item. kills squishies easy only when fed. can 1v4 if super fed. pretty much useless in other scenarios. jax/fiora/aatrox?