Final Fantasy 3: So I beat Saronia Catacombs, found a hidden area in the DS version, saw it gave a bunch of Elixirs and Phoenix Downs, proceeded to load up the NES version specifically to get those! I might be slightly overleveled in the NES version as a result, but I'm pretty sure bee-lining half a dungeon shouldn't make a big deal. This has been a useless comment, so onto the useful stuff!
-DS version gimped Doga's basement significantly...and I'm fine with that. It's a filler dungeon with the annoying Mini gimmick, albeit after Geomancers showed up so you have unlimited reasonable offense in both versions, well after that gimmick has over-stayed it's welcome. Thanfully this is the last time. NES version I probably made it harder on myself using Conjurer since the lower MP vs. Black Mage is really felt here, though again, Geomancers exist, so you use a few of those. Also NES version loved back attacks.
At this point, 3 possible dungeons to go to; to keep things fair, I tackle them in the same order in both versions. Sunken Cave -> Temple of Time -> Saronia Catacombs.
-...poor life decision in the NES version. The Sunken Cave stands out as a dungeon that the game NEVER tells you about, you just kind of have to stumble upon. Everything else has some hint, whether it's people in Saronia talking about a hidden passage to Odin, seeing a large ominous lake in the distance over impassable terrain, etc. In any event, the NES version, this dungeon is the hardest of the 3, probably intentionally so. Something I noticed is the Ambush and Back Attack rate is stupid high here, which I believe is something that Level helps prevent, suggesting that I tackled this dungeon too early. The enemies, while do-able, are clearly stronger than the other dungeons, the rewards are much better, etc. I believe the intent was they wanted you to do Temple of Time first, because the game spells out where it is, and then later you're suppose to go "hey, wonder what else is down here?" and find the Sunken Cave. Cannot say the same about the DS version, though the rewards relative to other dungeons didn't change (Air Knife is stupid amazing for Thief.) This dungeon is clearly easier than Temple of Time (not sure about the Catacombs), and offers rewards that help a lot there, like Reflect Mail for Fighters, Diamond gear, weapon upgrades, etc.
-Just going to note that rewards in both games for Sunken Cave are pretty stellar, and it's worth doing regardless. In fact, a key thing about the DS version is they buffed the Ancient sword a lot to be "just weaker than Defender", which makes Knights and Warriors way better, as that + the Defender Sword in the Temple of Time means they now have two reasonably powered weapons. Granted, Warrior wasn't TOO gimped since Axes exist, but generally prefers Swords due to weight issues. I guess I should note the NES version gives you the Blood Lance here, which is fantastic.
-Temple of Time is kind of lol-worthy in the NES version but probably because I just did a much harder dungeon before it. If I didn't, it'd probably be unremarkable still, since enemies just aren't scary. DS version? Ok, enemies are clearly frailer than the Sunken Cave, but the offense is way higher. Chimera's Lightning is a dick move, doing high 2HKO damage to any Fighter w/out Diamond Gear, and 3HKO damage to mages without Diamond Bracers, and you can be ambushed by 3 in a single fight. I thought those were just an anomaly...until I fought an enemy who cast Blizzaga on the party doing similar damage, and this is an element that can only be resisted by Armored units using a weak armor (Flame Mail); Sunken Cave's best attack is an enemy casting Blizzara for half that damage. Behemoths are in both but in NES version, they're shrugworthy, DS version, they're pseudo-bosses. A Pseudo-boss is something that appears pretty frequently in FF3DS determined by their solo appearance, high HP, and dual acting like bosses. Behemoth's Physical focused on a PC can kill them if they aren't a higher defensive unit; a Reflect Armor using Dragoon may not suffice.
Overall, I think the NES version definitely did it better. While the Sunken cave is a dick, it's at least optional and rewards you. The mindset probably was to scare people off with the powerful randoms who were un-prepared, as a "come back here when you're stronger!" means. This is not an uncommon tactic used in older RPGs, after all. Also, Sunken Cave is 100% optional, Temple of Time is required. Scaling one dungeon around the fact that someone MIGHT go to this other dungeon that has no reference whatsoever first as opposed to continuing the plot is poor design; by contrast, FF3 NES assumes Temple of Time is being taken by those who just left Doga's Mansion. I'd rather a dungeon be too easy because you did a side-quest earlier than they intended rather than a dungeon being too hard because they wanted to factor in those who did those side quests. Side-quests should be the harder dungeons, IMO, because they're optional. The point of them is rewarding you for taking the time to do them, not punish you for not realizing they exist.
-Saronia Catacombs...is uneventful. No, seriously, the enemies here are bland and easily killed, not much else to say. You could do this dungeon before Temple of Time in the DS version and get a lot of worthwhile rewards (there's a Reflect Mail and some Diamond gear here) and the dungeon is at least acknowledged, but I still don't think it's right to assume people find this dungeon before Temple of Time.
-Odin is way better in the NES version. A critical by him, which is more common than you think, can completely destroy a Viking, let alone a lesser armored unit, and Atom Edge is reasonable MT damage. Odin in the DS version is pretty much a large sack of health that hits twice for reasonable damage, who is only scary if he focuses those hits.
-I did steal Gungnir from Odin in the DS version, but I had to grind for about 30 minutes to get JLevels up for Refia (other 3 were killed off, so no benefit.) Thief Refia has been kind of broken since I got Air Knife; I saw her hit the 9999 damage display cap, albeit that was a Critical vs. an enemy weak to Wind. The massive JLevels for the Catacombs made that laughable too though i should note the JLevels didn't have an impact here, Saronia Catacombs are just not very good. This also affirms that yes, you definitely need grinding to get Gungnir, which hurts Dragoon's use. I'll probably stop using Thief since the last Locked Door segment is finished, and with the amount of JLevels, it feels unfair, though Thief also lacks any equipment upgrades until the final dungeon too, so using one despite it's damage can be a liability. Thinking of going Viking until Dark Knight gear shows up.
-Conjurer > Evoker. While Evoker does more damage on the damage summons, Conjurer in most cases does "enough" that it could one shot enemies, and Shiva/Ramuh are just so much better since their MT status' are extremely good while in FF3DS, I saw Mindblast hit like twice on one enemy, and Mesermize missed every-turn. basically, Conjurer is reliable because you know you're getting something good out of them, Evoker is 50% chance of deceny. To Evoker's credit, it definitely has the better Ifrit, due to the healing being exceptional, while the NES version's Healing is a huge pile of Meh. Then again, that's FF3NES vs. DS in a nutshell right there: FF3NES' status >>>> FF3DS' status, but FF3DS Healing >> FF3NES healing.