Requested by Super, here are projected rankings from where I'm sitting. Note that I'm giving two, one for the NES version and one for the DS version. I'm listing all classes just for objectivity.
For class names with dual translations and such, I'm listing the DS name first cause its the official translation; listing the NES name just so people who played only that version know what I'm talking about, etc.
Freelancer:
NES: N/A. It doesn't exist in any form here.
DS: Light. Bad damage and no real tricks worth noting. Decent defense isn't saving it.
Warrior/Fighter:
NES: Light. Pretty much the DS Freelancer.
DS: Heavy. Hits really damned hard at the cost of durability, and not bad on speed. The durability is debatably not an issue if he's slower than the opponent too for that matter (could be argued a quirk of the battle system.)
Monk:
NES: Light. More damage than the above classes, but less durability and still no real tricks.
DS: Light/Middle. Spoils Pure Physical PCs pretty badly, but otherwise, see the above.
Thief:
NES: Light. Pure Niche PC in game useful for out of battle purposes primarily, you tell me how its going to translate?
DS: Low Heavy. High speed, good damage, explodes to magic though.
Red Mage/Wizard:
NES: Middle/Heavy. Incredibly Tanky due to dual shields, with lots of status. God forbid it should face someone who forces it to rely on damage though.
DS: Middle/Heavy. More or less same as above, though status is worse, but healing is better.
White Mage/Wizard:
NES: Heavy. Healing and Status Galore, and some tricks like Reflect. Believe it or not, its damage isn't as bad as you'd expect (though its hardly good.) Naturally, some durability issues.
DS: Light/Middle. A worse FF4a Porom. MUCH worse.
Black Mage/Wizard:
NES: Heavy. See White Wizard, though, more damaging, Healing is worse but parasitic, and different status. Also isn't as elementally screwed on the damage end.
DS: Low Middle. A worse FF4a Palom...though not hit as bad as the White Mage.
Onion Knight:
NES: High Heavy. Have GOOD ITD or lose. Lacks damage or variety that is needed for Godlike, though.
DS: Godlike. The NES version adding in the entire DS Sage skill set *AND* status on its physical. Yes, this is as insane as it sounds.
Knight:
NES: Low Heavy. Cecil with more offense but no healing.
DS: High Light. Tank!!! That's about all he has going for him.
Ranger/Hunter:
NES: Low Heavy if you allow him the limited quantity Medusa Arrows (which Ninja wants to use too, mind), Light if you don't. Damage sucks, and White Magic it gains isn't all that good either.
DS: Middle/Heavy. Thief-lite.
Scholar:
NES: Light. Its a class that quite literally exists for one freaking fight in the game, what did you expect, competence?
DS: High Light. Has some minor healing, and some minor status...and averagish damage...and can hit magic defense...pretty poorly...basically, its a class that doesn't really translate into the DL, given its quirk (double damage from items) is something most won't factor in.
Geomancer:
NES: Light. Shouldn't shock anyone.
DS: Light. Doesn't translate at all; its quirk of basically being a Mage who doesn't need MP kind of fails. It'd be a Fun RPGmon class with that random chance of Shadow Flare though!
Viking:
NES: Light. Tank with little to no damage.
DS: High Light. Knight Variation.
Dragoon:
NES: Heavy. Jump hits really hard. Like, near-OHKO hard. Also 50%~ healing him since Blood Lance is awesome (and no, not useful on Ninja; Blood Lance heals FAR LESS without jump for reasons I won't get into, to a point where it won't make up for the damage loss in ANY scenario.) Basically, this guy is a massively improved Kain, that can't be stressed enough.
DS: Heavy. NES version but faster with some magic durability issues...oh, hits a little bit harder too, especially when not jumping.
Bard:
NES: Puny. ...its the Bard. Or more accurately, low damage, low defenses and no tricks.
DS: Puny. Uh, yeah, its the same thing just scaled to FF3 DS. Well, no, more accurately, its got a bunch of tricks! ...which do jack shit in the DL given what they do to his damage and all that. And when I say "what they do to his damage" I don't mean "Takes a damage nose dive" (cause 1/3rd average isn't bad enough), I mean "he struggles to do damage above 0."
...ok, he's a MAGIC TANK in this form, but pretty sure the 1/3rd average damage makes up for that...
...simply put, the Bard envies FF4o Edward.
Dark/Magic Knight:
NES: Heavy. 2HKO damage, if Dark Elemental, good durability, 25% Healing (!!!), and a few turn 2 potential "Auto Win" status.
DS: Middle/Heavy. The NES form w/ better speed, but far worse magic durability, lower damage (though still 2HKO) and no status.
Evoker/Conjurer:
NES: High Middle. Just shy of 2HKOing on average, and randomness factor hurts him, though, on average, he'll screw you over on turn 2. Durability can use work though.
DS: Light. Its the NES form, except now the damage is garbage and the status is really shaky instead of awesome. Uh, yeah, wonderful combo there...
Black Belt/Karateka:
NES: Light. Class that doesn't really translate in the long run, given his method of gaining damage falls behind what other classes get for weapons and such. Can kill frail healers with Build Up...most of which are in Light anyway...
DS: Light. See the NES form, only worse. Alternatively, take Monk, give it WORSE damage, and trade in the Anti Physical strategy for a 3 turn build up to a 2HKO!!!!!! Do I really need to explain what's wrong with this class?
Magus/Warlock:
NES: High Heavy. Black Wizard with better everything, including now gaining 2HKO damage.
DS: High Middle. A moderately worse FF4a Palom.
Devout/Shaman:
NES: High Heavy. Rosa trading in damage for being less reliant on one element, better speed (before Minerva), MORE healing, the potential to build up an actual Physical with haste (one casting makes it average damage! Yes, a Mage with average damage physical, BET YOU DIDN'T SEE THAT COMING!), and Wall that doesn't stop healing, but can't hit status either...think its a winning trade, frankly.
DS: Low Middle. When it comes down to it, while technically better, it still has every god damn issue the White Mage has. Eh, I'll throw it a bone, I guess.
If you're wondering, Magus has actual status rates and damage; Devout has shitty status rates (best one is 45%), and the damage isn't even half as good.
Summoner:
NES: High Heavy. OHKO damage with reliable instant death. IOWs, its Tir McDohl without the speed and takes hits somewhat worse!
DS: Middle. Average Damage and turn 2 instant death. One could say its a slightly nerfed version of the NES version...only slightly...
Ninja:
NES: High Heavy.High 2HKO damage and good durability. Also lots of status weapon options given it can use everything in the freaking book.
DS: Heavy. FF6 Shadow trading in the physical immunity tricks for the ability to take a god damned hit. Even trade overall, I suppose.
Sage:
NES: Godlike. The variety is absolutely obscene and nonsensical, it'll make your head spin. It also has OHKO damage, and no glaring flaws on durability.
DS: Middle/Heavy. Slower Devout who gets actual damage, and status rates...and far more status to play around with as well. This is such a winning trade its not even funny.
...one could say this game has a massive vote split <_<
Oh, a second opinion couldn't hurt, MOSTLY in terms of the mages. The fighters are all pretty straight foward, the Mages...its hard to judge given their variety and all. Its mostly the DS Mages I'm speaking about, mind; the NES Mages I'm pretty confident on (and most in particular, referring to Black Mage, White Mage, Devout and Magus.)