The extra dungeon and boss fight aren't anything to write home about though (if you have any experience with Squeenix's FF 1, 2, 4-6 GBA era ports, then you'll have an idea of what to expect; if not, then expect a long, grindy ass, megadungeon that adds nothing to the core experience, but is instead pure fluff stapled onto the side for those at the postgame looking for a way to level grind up to Level 99 or to make their capped numbers even huger; hell CT has hard stat caps that you don't need super dungeons/equipment to hit, and the ultradungeon utterly defeats the idea behind CT as a light and airy SuperNES era JRPG).
The SuperNES or the Wii VC versions are currently the most definitive experience, with the DS version on equal footing if you completely ignore the added content, followed by the DS version in its entirety, and lastly the PSX FF Chronicles version with its long load times and the PSN port of that version because it was already there.
Like the GBA version of FFVI changed things up so that you have a chance to get the Gold Hairpin from Lone Wolf in Narshe (or a last chance to learn Water Rondo in WoR) as well as infinite Ragnaroks/Illuminas(Lightbringers) later on (all it takes is to farm the motherfucking final boss). The Gigadungeon Dragons' Den was loaded with gimmicky 'even for an FF game' boss fights, trash mobs with capped HP totals and jacked up stats, ultimate weapons for every party member that were still weaker than Ragnarok/Illumina(Lightbringer), armor and accessories that weren't any more impressive than the stuff you could abuse the Colosseum for, and the Diabolo Esper for beating the final boss of the dungeon which teaches Quarter and Meteor or someshit. And then there was the Soul Shrine which was a 100 Floor Gauntlet which you ran in the hopes of gambling against the RNG for items you could take to the Colosseum to turn into Gem Boxes(Triple Stars) because having one super mage wasn't good enough (and by like Floor 60, they were diving into the monster pool from the Gorgeous Deluxe Collectors Edition Ultimate Dungeon Alpha 2 Turbo of the Seven Stars; and yes, it operated on "No Items!, Fox Only!, Final Destination!" rules).
TL;DR: SuperNES/Wii VC/DS (minus the extras) > DS (plus the extras) >>>>>> PSX/PSN.
