I don't think they're too bad honestly, and this coming from a huge fan of the series. VI is obviously the worst offender in many ways, but Nyxo's bilinear filter patch
really helps and steady progress is being made to mod the character sprites from the SNES version back into the game, which quells about 99% of the issues I have with it.
See here for a sneak peek
V's translation is much improved over the previous ports, and also benefits from having the bilinear character filter removed via a mod.
as for III, IV, and IV: TAY I suppose that's just a matter of personal preference. I liked the 3D versions of these games but wish the battles weren't hindered by 15fps performance. Obviously with IV and TAY we all would have preferred the fantastic PSP ports, but it's not like those aren't otherwise unavailable elsewhere.
The rest of the games (VII, VIII, XIII, XIII-2, and XIII-3) are are various degrees of from "okay" to "passable" ports but I think are all technically superior to their original console counterparts. IX looks like it will fall under the same category: not great, but passable and better than anything else available.
XI and XIV were always on PC so there isn't really much to talk about there in terms of porting.
It's a shame the series doesn't get more love in it's ports, but I'm ultimately happy with what's available.