In an effort to reduce the amounts of those kinds of threads that occasionally appear, this is here for all you experienced people to chip in.
Re: Post your input if it's helpful and not a repeat of what someone else says. Try not to make your input too wordy, but if it does, I'll give it a [spoiler] tag for ease of clarity.
Comments/tips/suggestions/etc. should be based on the entire class as a whole, not on a particular segment; i.e. don't say "brandish pwns" since it only applies to Heroes, which is 120 levels away from a new character and chances are a player might give up before even reaching it. If you must, do mention what class the tip does apply to.

FIGHTER/CRUSADER/HERO
Plays like an advanced Beginner
All about seeing high numbers, though the frequency of seeing those high numbers will progressively increase
Most skills are based on improving damage output
Versatility starts low and progressively gets higher
Lowest max MP, meaning potion choice is limited
No real supportive ability, albeit not needed for a purely offensive class
Uses swords and axes, though most use swords
Highest damage in one hit without damage buffs: 1560% / 3 monsters
Eye candy: (Advanced) Combo Attack or Shout
Comments from others:
Heroes are better on 2-3 monsters [than Paladins] -Flamez09
Crusader's Roar lets you focus on the more immediate monsters while keeping the other ones at bay with a momentary stunning. -KajitiSoulz

PAGE/WHITE KNIGHT/PALADIN
Dependent on elementally weak monsters (3rd job onwards)
Decent support ability (Threaten & stun)
Lowest versatility in terms of training spots
Supposed to tank better than Fighters, but tanking is useless in MapleStory
Possesses the only skill in the game that can stun unequivocally (Charge Blow)
Uses swords and hammers, though most use swords
Highest damage in one hit without damage buffs: 2100% / 6 monsters (uncommon to have 6 monsters bunched up)
Eye candy: Heaven's Hammer
Comments from others:
As a side note, the only place pages would have a hellish time training at is gobies and crimson guards. -Neonian
Paladins are better 1 vs 1 and 4-6 and Heroes are better on 2-3 monsters -Flamez09

SPEARMAN/DRAGON KNIGHT/DARK KNIGHT
Longest ranged weapons
Slowest attacking ability
Great at mobbing (3rd job onwards)
High support & utility, also acts as a battery (Hyper Body)
High versatility
Has skills specific to weapon type, unlike the other Warrior classes
Generally best tank due to Hyper Body
Uses spears and pole arms, though most use spears
Highest damage in one hit without damage buffs: 1530% / 3 monsters
Eye candy: Dragon Roar
Comments from others:

Dependent on elementally weak monsters (3rd job onwards)
Somewhat slow attacking ability They have the same DPS as fighters
Decent support ability Pages don't have any support moves
Lowest versatility Untrue, at lv70, Wks get 3 different paths to choose, and can change between the 3 whenever they feel
Supposed to tank better than Fighters, but tanking has limited usefulness in MapleStory Warriors in general can't tank
Uses swords and hammers, though most use swords
Eye candy: Heaven's Hammer
Comments from others:
none yet
As a side note, the only place pages would have a hellish time training at is gobies and crimson guards.

I think you mean DRAGON KNIGHT/DARK KNIGHT.

Tell that to all the Heroes who believe that Brandish has more DPS than Blast.
Threaten, as useless as it is, is still considered supportive, and Charge Blow's stun is supportive too.
WKs may get three different paths, but they are still severely limited in what they can do, whereas Crusaders can train in many more places than WKs.

I think its proven in 1 of these threads that blast is faster than brandish also paladins are better 1 vs 1 and 4-6 and Heroes are better on 2-3 monsters. Depends on which playing style you like the most. On the other hand White Knights train faster than Crusaders from 70-100 where as Crusaders train faster from 100-120 due to maxing coma and panic. Also since warrior elixers have come into play there isnt much of a difference between fighter and page other than threaten/rage. Same leveling speed from 1-70. With many people getting zakum helms early Fighters arent limited in the Mp department. All classes will use Mana elixers or Pizzas by 120

well i think that page/white knight/paladin are the most INTERESTING of all of the warrior classes, but my knowledge of the white knight and paladin areas of this statement are limited to only other's information. But with the three elements to choose from (four when you get to fourth job), i just think that it brings a whole new level of playing in. But that's just me.

I don't consider charge blows stun supportive, if you're going to play that card you may as well say that heroes coma (or panic, the mobbing one) is supportive since it stuns too, let's not forget wk's ice charge.

Wks can train in more places than saders because of ice charge, elemental advantage and ACB.

CB doesn't stun, it stops. Crusader stuns are pointless since the moment a stunned monster gets hit again, it regains consciousness.

lol @ WKs have more training areas than Saders... WKs are limited to monsters with a weakness, most of which are deserted and hopeless in terms of finding a party. Saders can train pretty much anywhere, and usually can find parties easily because of it.

For the longest time, Wks have more options for training spaces, they can go to ghost pirates, duals, kents, wolf spiders and such during low 7x, when saders are still at voo/hoodoos

dude a sader can easily go to those places during low 7x