If the fluff followed tabletop performance

Tactical Marines
Clad in power armour and armed with bolters, yet less well equipped compared to their contemporary adversaries.

A Tactical marine knows that the Galaxy is filled with enemies specifically designed to kill him, and acts accordingly.

Tactical marines make up for their lack of martial prowess by hiding in Flimsy metal boxes called rhinos on top of crucial objectives, occasionally firing from the top hatch in defiance of Universe that despises them. Their own commanders seeing fit to only give them the bare minimum of equipment they can afford, while the rest of the army goes about winning the war.

A tactical marine prays to the spirit of his Rhino, for should it be destroyed and he ends up within rapid fire range of an enemy close combat unit, his death is all but assured.

IMPERIAL GUARD chimeravets with melta, valkyries

The Imperial Guard are the technologically advanced and well equipped scalpelhammer of humanity. The standard guardsman is a highly trained veteran of many a campaign and has access to a diverse armory of arcane weaponry and transported in a durable and versatile armored transport whose firepower is the bane of many a lesser race.

Most feared by the enemies of humanity are the Guardsman's advanced, high speed, heavy armored skimmer transports whose firepower mocks the piddling weapons of lesser race's main battle tanks.

These are supported by an array of powerful missile systems to crush armor and sweep aside xenos hordes, and fast firing autocannons equipped with the galaxy's most advanced targetting systems to swat aside flimsy xenos fliers.

SUMMARY: highly trained, very well equipped. Technological advancement shows in high speed, high armor, high firepower transports, devastating support weapons and highly advanced targeters that neutralize enemy speed.

"their arrogance is only matched by their firepower, and their speed, and their armor, and their numbers... and yes the meltaguns too."
-Eldar commander after yet another terrible defeat


SPACE WOLVES
The space wolves are amongst the most feared of the Emperor's Finest, his space marines.
The Space Wolves boast the greatest number of psykers amongst any space marine chapter and it is a rare sight to see a space wolf host without numerous psychics at their head. Their psychic dominance is a great source of jealousy by weakling traitor marines and frail xenos.

The space wolves eschew close combat in favor of engaging in firefights where they patiently receive the enemy's charge. The standard transport of the space wolves is the razorback, a light vehicle with a powerful twin linked lascannon, able to transport a small squad of tank busting specialist wolves.

The devastator is the most prestigious position of the space wolves, armed with missile launchers they lay down a curtain of firepower across the battlefield with their advanced target selection training.

A famous variant of the space wolves is the thunderwolf cavalry. Unlike their brother marines these space wolves riding giant wolves favor close combat assaults, but even so these wolf wolves are often watched over by 30 or so devastator marines.

SUMMARY: highly psychic firepower army lead by librarians.

CHAOS
The twisted forces of chaos are set in a heiarchy where the beautiful rule over the ugly. The bloated forms of cannonfodder plague marines contrast starkly with the inhuman, nay, otherworldy perfection of their daemon prince masters. The lumbering, misshapen forms of obliterator marines also submit to the allure of the Slaaneshi lords.
Ugly, stinking nurgle marines march forward into the enemy to protect the flawless form of their masters for their very lives are not worth marring such chaotic beauty. The princes of chaos then use their dubious sensuality to bewitch their victims into gimps that crave the lash of the obliterators firepower.

It is unknown where Slaaneshi lords emerge from as they seem to spontaneously appear to lead their aesthetically impaired minions.

SUMMARY: beautiful demon-god sadist and his fat, ugly masochist minions.

Orks

Ork Nobs scoff at lesser races attempts at protection on the battlefield. For while their enemies try to protect themselves with primitive power amours, and arcane fields the Orks know that the only real way to cheat death on the battlefield is to carry as much differant gear to look as unique possible. This is why all Nobs need to organize before the Waaaghh to make sure no two are wearing matching outfits.