So just bugfixes, right?
-With FFI you should probably be looking at FF Restored. Not a fan of the font? Rodimus Primal made a patch that brings back the original FF font.
-II and III I don't think have anything outside of translation patches.
-FFIV is generally Project II or Namingway Edition, depending on how you like your text and stuff.
-FFV doesn't really have much, fan translation or script port? The latter has other bugfixes in an optional patch.
-FFVI generally has Ted Woolsey Uncensored being the top recommendation for non-game changing stuff from what I have heard, and it already has most of the big stuff rolled in. If you don't want the text altered, check out these two posts for SNES and GBA patches that have every single little bugfix (over 180 for SNES) rolled in: https://www.romhacking.net/forum/index.php?topic=25372.msg365789#msg365789
-Chrono Trigger: I don't mean to brag, but I think Bugfix and Uncensoring Patch is what you're looking for? If you're not keen on text altering, there's a patch for the racing minigame. That is the one gameplay bug you're going to notice in CT.
I'm still confused about whether Flames of Eternity is supposed to be preferable over Crimson Echoes.
Flames of Eternity is billed as a continuation, but one that is generally viewed in a bad light because: a) they rubbed out any mention of any of the old staff, b) they use it to sell stuff, and c) they threw in a lot of stuff that was never intended, with about the results that you'd expect.
Think the opposite of Pokemon Prism here, where that team just wanted to fix bugs and complete what was intended while still giving credit where it was due.